I really just kinda feel like commenting on a lot of characters and not just who I think will be good. Anyway, here I go:
Crimson Viper is an incredible force to be reckoned with so I’m sure she’ll still be one of the best despite requiring a bit of extra effort to make work. She doesn’t seem to have been toned down at all in Ultimate which is kind of unnerving.
Dr. Doom wasn’t bad at all in normal Marvel 3, but in Ultimate he seems to have only gotten better, so he’s definitely going to be a scary one. His new jumping :s: is absolutely ridiculous among other things.
Trish and Zero are two of the most annoying characters in the entire game as far as I’m concerned, and neither of them seem to have been hit too hard. As far as I can recall Trish hasn’t gotten worse in any regard and while Zero has been changed in various ways he still poses a great threat. His new Buster is going to be something.
Dante will still be a solid contender regardless of the fact that he’s been toned down a bit. He might be out shined by his brother this time around, but Dante is Dante. I don’t really see very many people dropping him. Vergil really does look good, if not a bit overrated currently.
It appears that in the areas that they’ve toned down Magneto’s rush down they’ve upgraded his defensive game. His gravity related specials will probably be rather annoying to deal with for certain characters.
Amaterasu is still solid despite the air dash change, but I think that just means that Amaterasu players are just going to have to play a bit smarter. That’s not necessarily a bad thing. Air weapon switching will be rather interesting to experiment with.
Dormammu’s changes seemed to be indicative of statements made by Capcom that zoning is becoming a more viable playstyle in this game. Dark Matter ( :f::h: ) special cancel and aerial Dark Spells change up things a lot.
I’m not sure how Jean is going to end up in Ultimate. She’s coming in with even less health, a single action per air jump, and her TK shots disappear when she gets hit. Needless to say she’s been toned down a lot. Dark Phoenix will still be a force even with changes to X-Factor but I do think the game has been leveled quite a bit.
Wesker and Wolverine are still going to be good. Not much else to say about that. Meanwhile Haggar, Tron Bonne, and Hsien-Ko don’t seem to be getting what they need to be viable point characters.
The developers appear to be only concerned with Haggar and Tron’s assists and completely ignored how weak they were as point characters along with Lei-Lei. It’s rather unfortunate, but I hate Tron anyway. 
Speaking of characters generally being ignored, what’s up with Viewtiful Joe only getting one new special move and a mashable Mach Speed hyper for more damage? Everyone has a mashable hyper now, so that barely even counts.
Seems like Capcom still insists that Viewtiful God Hand is enough to make the little guy a serious threat. We’ll see how his new Slow Dodge ( :s:+:atk: ) changes things. Still sad about no OTG
Red Hot Kick.
Firebrand is someone I’m really excited about and curious to see how he’s going to fare. He seems to have all the necessary tools needed to be a viable character. New Wolverine? Maybe not, but definitely a good character.
Nemesis doesn’t look good to me. It just seems like he’s going to get zoned out hard and punished every time he makes a move by other, more defensive oriented characters.