Well there are a lot of factors, so here they go:
*No X Men: X Men always have been a great part of the franchise, after all the franchise originated with the game X Men: Children of the Atom and Capcom Vs, X Men. So having then removed feels wrong, in this series the equivalent of Ryu and Ken is Ryu and Wolverine, and there is no Wolverine in this entry, maybe later as DLC, that is like I said making an Street Fighter game without Ryu or Ken.

Art direction and Style: this series has always had a super stylized art direction that reflects its comic book heritage,all colors flashy attacks, etc, this entry’s art style is trying to emulate the Marvel Cinematic Universe, so they are trying to make the character realistic, this has led to an really bad art direction that looks straight out of a mobile game, most of the character look like cosplayers, and the setting looks dour.
And finally this is the most important, the game feels rushed, and it probably is, it has been developed really fast, and is suppose to release in a couple of months, but the game-play, looks of the game, everything feels rushed, or at least in demo that people played. For comparison DB FighterZ, plays and looks way better than Marvel Vs Capcom infinite, and the developer said that they are only 20 % done with the game. That tell us that Marvel infinite is technically inferior to an unfinished product that is only 20% done, and that DB FighterZ will be amazing if this is only 20% of its power

As much as I love making jabs at MvCI because looks about has hype as a flaming bag of dog shit, I know deep down that I'm just using humor as a coping mechanism to try and deflect my sorrow away from the fact one of my favorite fighting game franchises is becoming a flaming bag of dog shit.