Generally people agree that most Marvel characters are 'grounded', at least moreso than DC's, and that 'too' powerful characters rarely affect one's enjoyement of a story. When you look at Spider-Man and his villains, you do get the feeling that Peter won't just walk over his adversaries.
There are however a few heroes whose power-levels, IMO, are starting to get out of hand or have already.
Thor- Yes, he's always been powerful, some would argue that he's already been depowered, but I can't help but to notice how he always seems to be the guy to either finish a threat or lead the charge against the most powerful opponents. Oh, the time-stream's collapsing and Galactus is destroying the city. Have at thee! Janet's actually a living bomb, we're all going to die in a minute. No problem, Thor'll just send her into another dimension. The Sentry is going berserk. Thor'll handle it. Sometimes you can't help but to wonder why the other Avengers even bother.
The worst thing is how many people seems to be fine with this. I guarantee you, if you make a rumbles-thread with 'Thor vs X', most people will vote Thor almost by default. I mean, how many times we've heard about the 'Berserker's rage'-thing and strength-doubling belt and whatever. Thank jeebus he doesn't have the Odinforce anymore. I accept the fact that he's a god and he should be powerful, but IMO he should have no business messing with Galactus.
Hulk- He's the strongest one there is. Fine, but when I hear people claiming that he can get so angry, so strong, that his punches will tear the fabric of reality apart, I can't help but to shake my head. Why won't you just make him a reality-warper while you're at it. There should be some kind of limit to what you can do with pure physical force.
It's not the Hulk's strenght that even bothers me. It's his invulnerability. He's not only resistant to pretty much everything, but he regenerates faster than Wolverine. So how do you kill him then? Even Superman has kryptonite and magic to look out for. I've heard that Hulk can even resist molecular/reality manipulation. That just seems like overkill to me.
Wolverine- He's a guy with a metal skeleton, claws and a healing factor. C'mon, even I could kill him.
Iron Man- Ok, he's not that bad, but I just don't see why he should be in the 100-ton range.
Steve Rogers- I've said this a few times before and I'll say it again: he needs to lose to someone. Badly. No, not just a he-lost-due-to-some-small-factor-and-comes-back-later-to-get-payback- kind of defeat. Just a thorough ass-kicking.
So, can you think of heroes(villains too) that should get knocked down a peg or am I just spewing crap?
EDIT- "Depowering" doesn't need to mean removing or completely altering abilities, just keeping consistency on how they're used, or alternatively writers not playing favourites all the time.