Htydjtk

There are many beings that have very big powers. There are beings that are worshipped as gods (Asgardians; and I would lump Azazel into that as well since Marvel seems to imply that he's - while a mutant - someone people consider to be "Devil"). There are mutants whose power would clearly have been considered as "god like" by people worshipping Greek or other polytheistic pantheons where the threshold to what made you a god was pretty low.

But are there any actual major "Gods" in Marvel universe?

Since there are many different definition of what a "god" is, the one that is pertinent to this question:

1. Power wise, being able to create Universe(s); e.g. gods more in a sense of Christianity/Judaism scale rather than "Pan" or "Hestia" in Greek pantheon who merely have some limited supernatural powers over small domain of natural events.




2. Effectively immortal, at least excluding specific exotic attacks.




3. Origin-wise, be "supernatural", not merely a human mutant or a powerful alien with advanced technology.




4. Desire/demand/like followers' worship or prayers.

One-Above-All

There are many "gods" in the Marvel Uni/Multi/Omniverse, but presumably the most powerful is the One-Above-All, a mysterious entity said to be the "creator god" of Marvel, and has once been implied to be Jack Kirby, the then-partner of Stan Lee and co-creator of many characters, who was represented in a Fantastic Four comic (issue #511) as a god-like entity who took the form of a "comic book artist" looking very similar to Kirby (though this is probably unlikely).

This picture comes from the Marvel Wikia.

Elder Gods

Next, there are the Elder Gods, listed as the "first kind of gods" who were created by the Demiurge, another cosmic entity living as the sentient force of Earth's biosphere.

An image from Comic Vine:

New Gods

The New Gods are immortal, human-like beings that are not as powerful as the Elder Gods. Known New Gods are worshipped by Earthlings. The likes of Odin and Zeus, among others, have sometimes been referred to as "new" gods, but whether or not they are is debatable.

Celestials

Maybe not "gods", the Celestials were born at the birth of the universe, and created life, death, and apparently the multiverse itself. However, they restricted all interactions with humanity long ago, and thus humanity has all but forgotten them.

The leader of the Celestials is called the One Above All (without hyphens) and, like the rest of the Celestials, he may or may not be an actual god. However, he is not to be confused with the One-Above-All, the actual creator god listed above.

Some Celestials:

Gods by Race

In the Marvel Universe, many different races of humans and other species worship many different entities, classifying them as "gods". This list can be seen here. This includes Norse Gods, such as Thor and Loki, and Skrull Gods, such as Kly'bn and Sl'gur't.

Examples:

• 
  Storm, the weather-based member of the X-Men, is worshipped as a goddess in Kenya.


• 
  Beta Ray Bill, a being with Thor's powers, is worshipped as a Norse God in some places, but is by no means a Norse God.


• 
  Selene, the "Black Queen", is worshipped as a goddess in Marvel's Nova Roma.


• 
  Demons, former Elder Gods, are still worshipped as gods by some.

Conclusion

There is more than one "god" (millions, in fact), as classified by your standards; however, there is only One above all.

Think of it like this (if you are a Tolkien fan): One Above All is to Marvel as Eru Iluvatar is to Middle-earth.

Cosmic beings capable of creating or manipulating entire universes, who desire worship and are almost immune to attack, litter the Marvel Universe. It would seem whenever Marvel needs a universe-threatening menace they create a new one to add to their already existing pantheon.

These beings in order of power (as defined by Marvel):

One-Above-All

The most powerful of Marvel's supreme beings uses an appellation that has been applied to two entities. To distinguish them, the Supreme Being is dubbed the One-Above-All (with hyphens).

• The One-Above-All (not to be confused with the Celestial with the name, The One Above All) claims to be the first and most powerful entity in the Marvel Omniverse.




• The One-Above-All has another potential identity as The Fulcrum. The Fulcrum is also the Bartender who runs The Vestibule, a swinging bar where Eternals go before they either return to a newly regenerated body or head off to Lacuna (The Afterlife). Said to be "all-powerful" and "all-knowing", the Fulcrum is likely an aspect, manifestation, or alternate name of the One-Above-All.




• He is omnipotent, omniscient, and omnipresent. He is the most powerful being in the Marvel Omniverse. His power is unlimited, incalculable and immeasurable.




• The Living Tribunal: is considered to be the right hand to the One-Above-All, he is the cosmic arbiter of what is right in the Multiverse and is capable of dispensing justice as he sees fit.

• Undoubtedly the most mysterious character within the Marvel Omniverse. The One-Above-All has only appeared and been mentioned a few times. He is not to be confused with One Above All, the leader of the Celestials, or any religious figures. The One-Above-All was first mentioned by the Living Tribunal when Doctor Strange first encountered the entity. The One Above All is often unofficially cited as Marvel's creator. ~ComicVine
  

The Beyonder

As much as it pains me to do this I must include the entry of The Beyonder. Despite his hokey and completely contrived origin for the Secret Wars Sagas, he has by virtue of materials written about him after the Secret Wars, the second most powerful being in the Marvel Multiverse. I will keep it brief:

• 
  The Beyonder was originally from an infinite realm beyond the Marvel Multiverse, called the Beyond-realm, and was the sum of everything outside the multiverse (our multiverse was a drop in the sea compared to the Beyond-realm). It became self aware and formed a being of immeasurable power. (He was originally described as millions of times more powerful than the entire multiverse.) ~Comicvine
  

• The Beyonder was, at one point in his history more powerful than all the conceptual beings in the Marvel Universe and even manages to kill Death itself.

This picture shows The One Above All (Celestial), The Stranger, The Living Tribunal, Master Order and Lord Chaos, Eternity, The Watcher (lower left) The In-Betweener (in black and white) The Beyonder (in the orange jumpsuit), Mephisto (in red) and Death.

The Beyonder was vain, arrogant, annoying, petty and capricious. But there was no denying his powers. At his peak he would have certainly been considered omnipotent, his raw power having the ability to do anything he wanted, but he lacked a clear understanding of the Universe so he is not omniscient (unless he wanted to be) and not omnipresent (unless he thought about it).

One final note: The Beyonder has been retconned MANY TIMES. His origins are no longer clear to anyone and his recent appearances claimed he might be a mutant or he might not. Don't think too hard on it. If you're lucky, you'll never see him again.

One other note: The Molecule Man who depending on when you ask, derived his powers from the Beyonder or the Beyonderverse as well, so he would also be in the same class as the Beyonder, capable of creating entire universes if he so desired. He's currently dead, but since he has resurrected himself in the past, his death is "relative" and likely not permanent.

Galactus, The Devourer of Worlds

• Galactus, The Devourer As Galan, Galactus is the only survivor of the universe that existed before the Big Bang. He was actually born billions of years ago on the planet Taa.




• Galactus was the sole survivor of the previous universe and whose presence and absorption of worlds was learned to hold back the destructive capacity of the fourth conceptual being named Abraxas, the embodiment of Universal Destruction.

The Eldest

The Eldest: The four oldest beings/forces in the Marvel Universe. They are the First and arguably the most potent forces to exist in the MU. They view each other as siblings.

• Death or Mistress Death was the first power to exist after Galactus. Death is one of the most powerful beings in the Marvel Universe. She often appears as a skeletal figure in a purple cloak but can appear as whatever she wishes. Mysterious, she almost never speaks and rarely makes personal appearances. For a time, the mad Titan Thanos, sought to kill half the Universe, using the Infinity Gauntlet to win her favor.




• Eternity and Infinity: Cosmic entities capable of shaping reality as they see fit, since it comprises their very being. Almost nothing is beyond the capacities of these two beings, but they rarely interfere in the day to day operations of the Universe-at-large, recruiting agents such as Doctor Strange to do what must be done, since if they do it, they have the potential to disrupt wide swaths of their own internal reality. The equivalent of using a nuke to kill an insect.




• Oblivion: is the personification of entropy which is the collapse or death of the universe. He is the male counterpart of Mistress Death. He has created many avatars or agents including Malestrom, Mirage and Deathurge. He is devoid of matter and energy and only seeks to return the Universe to the nothing that it was spawned from. Not invited to many parties.




• Abraxas: The embodiment of universal destruction, a being whose powers rival the other three and is capable of envisioning and completing the destruction of an entire universe using the Ultimate Nullifier. This is an incredible feat because he has to be able to envision the universe in its entirety before using the device. He is also able to resist being destroyed after using the device.

While these beings can take on humanoid forms, they are NOT even remotely human. Their power is so great, even seeing them in their raw form can drive mortal lifeforms crazy.

The Cosmic Beings

Cosmic Beings, also known as Abstract or Conceptual Entities: These are the beings which form the underpinnings of the Universe and help to bring order out of the cosmic chaos.

• The Phoenix Force as the Embodiment of Life is considered to be Death's antithesis. Her powers of creation and destruction are without peer and she (while wearing the form of Rachel Grey) fought Galactus to a standstill.



• 
  

  Master Order and Lord Chaos: These two are the living embodiment of Order and Chaos in the Universe. Lord Chaos and Master Order always exist together in the cosmos.

  
  
  
  
  

  • Lord Chaos asks Master Order questions and Master Order attempts to answer them to Lord Chaos' satisfaction.

  
  

  • Their agent in dealing with mortal beings, who helps maintain the Universal Balance between Order and Chaos is the In-Betweener, a being in between all conflicting concepts and thus immune to almost any form of harm by most mortal beings in the Universe.

  
  

  • These two are not above recruiting lesser beings to restore Order (or Chaos) to the universe if necessary.

  
  
  
  

There are others entities who embody other cosmic concepts such as Master Hate and Mistress Love. These are not lifeforms, they are conceptual beings who play some part in the maintenance of the functions of the Universe. In the case of Shuma-Gorath and the Many Angled Ones, they are part of some underlying fabric of the Universe formed after its creation.

There are also at least two artifacts capable of similar universe-altering transformations. Both were believed to be artifacts of the One-Above-All.

• The Heart of the Universe: The Heart of the Universe is an object of infinite proportions. It's possession makes the user the supreme being of the Marvel Universe capable of shaping reality as they saw fit. The Heart of the Universe was presumably created by Marvel’s Supreme Being to correct an imbalance in the fundamental architecture of the Marvel Universe.




• The Infinity Gems: The Infinity Gems are six precious stones of cosmic origin that give the possessor mastery over a certain power. Collecting and using all six gems will give the wielder complete control over the universe. Only the Living Tribunal, judge of the Multiverse, is immune to the wishes of the wielder of the Infinity Gems.

There is one example of a being that is a God though I'm not sure it falls into 4th criteria.

It's known as One-Above-All.

It's considered to be the creator god.

http://marvel.wikia.com/One-Above-All_(Multiverse)

Apparently responsible for the existence of all life in the Multiverse
and possibly beyond, the One-Above-All is the master and sole
superior of the cosmic overseer and arbitrator known as the Living
Tribunal.

Official Handbook of the Marvel Universe A-Z #6

His Powers and Abilities are pretty much unknown but being the creator of the Multiverse he would have these :

As the supreme being of the Omniverse, the One-Above-All is
Omnipotent, Omnipresent, Omniscient, and Omniversal, above all cosmic
powers and abstract entities, even the Living Tribunal.

Image of The One Above All

_{(source: nocookie.net)}

Fun quote from Mephisto regarding perhaps this being :

When a bartender asks the demon Mephisto whether the Living Tribunal,
having created the Infinite Embassy, was actually "God", Mephisto
responds, "No, he's not God. He's just the biggest kid in all the
playgrounds. And if he knows the Principal, he's not exactly chatty
about it."

Journey into Mystery #627

And The Living Tribunal said this to Protégé :

When the Protégé claims to the Living Tribunal and other cosmic
entities that he is the most powerful being that ever was, and that he
will surpass them all and move up, the Tribunal counters, "Impossible!
There is only one above the Living Tribunal!" Later, after the Protégé
declares himself the One-Above-All in an attempt to seize ultimate
power, the Tribunal absorbs the Protégé into itself, proclaiming,
"Your actions and intentions are inexcusable! Make your peace! May the
One-Above-All forgive you!"

Guardians of the Galaxy #47-50 (1994)

The only appearances of it according to that wikia are in Sensational Spiderman Vol 2 #40 and Shadowland Ghost Rider Vol 1 #1.