There are some... hyperbolic opinions in here.
First off, this trailer was 1:30 minutes long so I'm not sure how someone is to know everything they need to know about the game from that.
This game is being developed by Team Ninja who have a pedigree of making combat focused games, games in theory very similar to Marvel Ultimate Alliance, they have worked on the Warrior's franchise, Ninja Gaiden, Dead or Alive, Nioh to name a few. Actually if you actually look at their history with games that empathize combat, really you should be less concerned when you consider they have more experience than Raven Software did before XML2 and Vicarious Visions for MUA2 who had only worked on middling licensed games before hand.
Regarding graphics, could they look better in quality? Absolutely, but the idea that because they're stylized that this is now a kids game is such a bizarre concept to me, it reminds me of when people thought Wind Waker was gonna be a 'kids' game because it was cell shaded. Also the idea that MUA was ever a super violent gritty game in the first place...
Regarding roster, all the press releases for the game promise a big roster, and they specifically mention the X-Men and others in it, so I'm not sure why we are not waiting to see who else is added before being outraged, MUA and MUA2 certainly didn't reveal their entire rosters in their reveals. Yes the initially showed roster is 'MCU' heavy but lets face it
most of Marvel is in the MCU so I'm confused why people would think otherwise, they want the game to sell. I'm sure we'll get fan favorites down the line.
Most of the characters here are also wearing comic looks so....? And the majority of Team Ninja's previous games are known for having a lot of costumes so there is that.

Also I'm gonna parrot Polygone as well, the idea that the past games were some gleaming beacon of level design is a little rose tinted to me, yes MUA has some good levels it also has some bad, generic ones. MUA2's level design was very stale and XML2 like they said, was literally just sewers and grey corridors.
I love these games to death, but the idea that they are perfect games, at the time or even now is... bizarre.
I get that at first glance this isn't the ideal MUA3 we probably had in our heads all these years, but outside of graphics, which apparently seems to be the main basis for concern, it's still early so I don't see why people don't wait to see how it progresses before writing it off.