Had the house to myself tonight so I got to go see...
I quite liked it a lot! I mean, the entire plot is about as by the numbers as you can get. You can see every single story beat coming a mile away, but it works because the cast and writing are strong enough that its just entertaining regardless of the dumb as bricks plot.
I think nailing that part of it was also probably the biggest challenge. You know, when you watch all the movies these guys came from, thematically they're all very different. They're all shot different from each other, they look different from each other. You don't just watch them and think "Okay yeah, these are in the same universe." So to make all those characters click really is quite the feat. Iron Man is acting like Iron Man, Cap acting like Cap, they're all playing their parts the way they should. The only one that's a bit of a wild card is The Hulk. He's been changed quite a bit to work here, and it is certainly for the better. Hulk is easily the secret best part of the entire movie.
Casting Ruffalo was a really smart choice. I don't think Norton could have played this Hulk, and looking at the way he was written, I'm assuming this is why Norton became a big bitch and wanted out because of creative differences. Good. Ruffalo had fun as Banner, and he just carried a completely different persona while still staying true to the spirit of what makes him tick. He's almost like a hot headed Peter Parker here, not so much a dead serious dude on the run. He has a certain charm to him, as both Banner and Hulk. There is a huge, HUGE build up to the first time he changes, and the pay off was just amazing. I also liked just how damn important he was to the plot as well.
I didn't care for Hawkeye or Black Widow. They both had some fun moments, but if they were smashed into pieces at some point during the film, I wouldn't have given a shit. I didn't really care about Thor either. I really wanted to watch Thor before seeing this, but now after having seen this, I don't really care to go back and watch it. I had enough Thor in this movie, I don't need to see more Thor. He's boring.
I also kind of respect how this movie just knew what it is, a big fun comic book film. It is not grounded in reality in the slightest, and they make the most of that. There are moments where it really does feel like a comic or cartoon just come to life. Stuff like the secret ending scene after the credits (the second one) just drives that point home even more. Oh yeah, and that long take toward the end that panned around all the action to each of the heroes was really impressive. It's not a "true" long take, there was obviously lots of compositing and transitions and different shots all being inserted into what seems to be one take, but it doesn't make it any less impressive.
So yeah, it's fun and worth watching. Certainly not mind blowing, but easily the most enjoyable film to come out of Marvel Studios next to the first Iron Man.