10. Coulson's Alive?
I know, it's hardly the most original point to start with, but I couldn't do a list of criticisms and not include Phil Coulson's Lazarus-esque feats. Granted, within the film itself it works really well, so if you take this film by itself, Coulson's death works extremely well as the nadir out of which the heroes have to climb. But that's the thing you can't take The Avengers by itself. It exists as part of a continued canon, so anything later on can sneak up on Marvel's show-pony and hobble it a treat. So when the admittedly cool trailers for Agents Of Shield came out and made a huge point of resurrecting Coulson ('welcome to level seven, etc.'), it blows our mind for three seconds but leaves up with a head-scratcher every time we boot Whedon's opus (yeah, you heard) back up. After all, that was a pretty convincing death rattle from Clark Gregg.