Good movie, definitely a few trademark Whedon moments. I don't think it's as good as some have been rating it though (8.8 from 65k votes on IMDB, wtf?) - it's not THAT good.
I also feel they missed a trick towards the end - and was even half expecting them to do it, too...
What happened to the rest of the Avengers?
How awesome would it have been if - even if in one brief cameo shot each - you had the Vision, Quicksilver, Wonderman, etc. etc. coming in from somewhere to join the battle. Or even grabbed characters from other linked sources, like throwing the Punisher in the mix in some fashion or other. Again, it wouldn't have had to have a crazy backstory or anything, like they could have just played it out as Nick Fury using his 'secret weapon' in sending out an APB to all Avengers across the globe, or something. That might have made it 8.8 worthy.