A third-person action game a la Batman Arkham would be the dream for me, but it's hard to imagine that working well with all the different power sets and play styles that would be involved. I just hope that we actually will be playing as the Avengers and not creating our own character for an online game or something like X-Men: Destiny. I think we can rule out the former, though, given the developers.
I think I would prefer it if they kept the "game universes" separate, though. Perhaps games from certain developers could share a continuity and form a franchise, etc. but I wouldn't want everything to be connected and tied together. It's one of the things I actually dislike about the MCU because of how they constantly promote and remind us that they exist in a shared universe. I mean, yeah, it's fun to see Ant-Man outsmart Falcon and whatnot, but to constantly have them talking or even just mentioning the Avengers and whoever else is pretty annoying. Plus, that would be much less restricting and allow other versions of certain characters and groups to exist and serve whatever purpose the story may need.
That said, I would still love to see Spider-Man show up here, or other heroes. My preferred roster would be the original New Avengers, but that's obviously not happening because of the ban.
Regarding the narrator in the trailer, I thought it might be Ms. Marvel too. Definitely sounds fairly young, and I would love to see her be the one to reassemble the Avengers, considering how much she loves and admires them. Although, well, not so much currently, I guess. It would be a pretty fantastic move too, I think, considering how popular the character is and what it could mean to have her as the lead character. Seems too good to be true, though. But hey, wouldn't be impossible.