After seeing this, the preview for this isn't quite as impressive.
Don't get me wrong, I want to see Avengers, and I think it could be a real fun, especially given the personalities of the ensemble cast.
But after seeing Act of Valor's uber practical effects (it's hard to beat real seals using real weapons, with real ammunition, being moved around by real vehicles (like a frickin Ohio). Even the blood and gore effects were practical.
It really shows the extreme verisimilitude practical effects and cast members that know what they're doing can bring over CGI and actors.
And here's a bit of behind the scenes for Valor.