Well, to fall back on the old cliches, European cinema tends to be thought of as more self-conciously arty, more concerned with visuals and ideas and less concerned with plot and narrative. An easy shorthand for me is that Alien (directed by a Brit, creatures designed by a Swiss guy), is, in a lot of ways, a European film. Impeccably designed, beautifully made, filled with haunting imagery, but with a simple plot, thin characters, minimal dialogue, etc.
Whereas Aliens, though made by a Canadian, is a very American film -- tons of memorable characters and memorable dialogue, but much more fast-paced, action-packed, story driven, and much less about mood, suspense and ideas than its predecessor.
Whedon is a huge fan of Cameron and Aliens, and he fits into that lineage to me, as does his film -- he even said Cameron is who he studied for the action scenes. So my feeling is if European critics are embracing a very "American" film like Avengers, American critics might like it even more. Make sense, or am I reaching?
ETA: Yeah, no way this drops under 90 percent at this point. Just closed Tribeca to more raves from cineastes and film snobs. Paul Haggis called it "surprisingly satisfying." 91 is the lowest it's gonna go, I think. I'm gonna stick my neck out and say it manages to stay at 95-96 though.