This looks really bland, in my opinion. I'd agree, in isolation the mechanics do look decent, but it looks like the objective for the devs was "Make GoW2017 work in the MCU", which really isn't exciting. It really does feel like a movie that they have tried to add some interactivity to. Some thoughts per character:
Thor - This looked okay. Ground combat seems very simple, although I like that he has launchers and air combos. The hammer throwing mechanics could work like a more interesting version of GoW's axe throwing. I hope he has more than one combo string without the hammer though.
Iron Man - I get the feeling that you get XP for every kill to try and make you feel like you aren't wasting your time. Aside from the visual spectacle, nothing about the on-rails/shmup gameplay looked particularly interesting. In the second section, I do like his air dodge though - hopefully he has more interesting movement options in the full release.
Hulk - I like how you can use enemies as weapons, and you can grab two and pummel them against each other. I suspect there will be some opportunities to cause a lot of destruction on-screen with Hulk, which could be fun. The gameplay looks too simple and bulky for him to be a properly enjoyable action game character for my tastes.
Cap - I think this was my favorite gameplay out of the bunch. Cap looks reasonably agile. The shield throwing looks like it allows for pacier combat than Thor's hammer throw does. At a glance, it looks like he has more variety in attacks than the other characters (aside from maybe BW), but it's unfair to judge based off of one video. Might just be me, but I felt like his attacks were a bit meatier than the other characters. I really hope there are more ways to deal with the shielded enemies than just throwing your own shield at them over and over.
Black Widow - Most of this section looked poor. We start with an incredibly long set-piece/QTE section, only for the next section to require you to dodge the same attack over and over until you fire enough pistol shots at your enemy. Once we get in to the boss fight, things look better though - more like Cap's gameplay. Hopefully this part of the game is just a poor representation of what the character can do. Looks like it uses the exact same parryable/unblockable indicators as GoW did.
It certainly has potential, but I guess we'll have to wait and see what comes out of this. The set-pieces/QTEs, XP system and general "cinematic style" gameplay (it basically looks like it plays itself) leave me less than hopeful. Ultimate Alliance 3 is looking like the stronger Marvel game so far.