MVC2 was both a budget job (I feel) and severally limited technically (I know).
The reason most characters looked so stiff and ugly when moving is that they had to cut a lot of frames to get it running well.
Sentinel in particular seemed to lose a lot of detail (and even some unique attacks) in the long transition from COTA to MvC2. And he definitely wasn't the only one to suffer.
MvC2 was a hack-and-slash job that crammed as many characters into a project with seemingly significant budget or time constraints. It's as if Capcom was determined to fit in as much as they could into a single game while they still had the Marvel license. Visually, it's a jarring mess of old CPS2 sprites from different source games with significantly different art direction slapped on top of unfitting 3D backgrounds. Thematically,
nothing in the game aside from the characters themselves evokes anything about Marvel or Capcom. Any effort put into that game went to the roster size and the gameplay; artistically, it certainly gives off the impression that it was a budget job.
On the other hand, when it comes to aesthetics alone, I think MvC3 is one of the stand-out games in the entire genre. (Guilty Gear Xrd or Vampire Savior would probably take my crown for most impressive overall, fwiw.) I don't know if there's anything in particular that "wowed" me in Marvel 3, but pretty much everything about it is slick and meshes well together. The character models, particle effects, and general art direction are all on point. The stages and final boss at least pull a lot from the actual Marvel and Capcom universes, which is more than can be said of MvC3's predecessor. And there's all the little touches like the team-specific tag calls or the plethora of matchup-specific dialogue (which not even SF4 had... unless you were playing in arcade mode, for some reason).