The Avengers is an incredible movie, not just a great superhero movie but a really good film. Marvel has made a big gamble with this picture and it has paid off. The movie starts off with an introduction to each of our heroes and their antagonist: Loki. It's all pretty usual stuff from here. But once the heroes come together, the movie becomes something more. There are a lot of big egos flying around and each one is more used to being the centre of attention, especially Robert Downey Jr.'s Tony Stark. It's in these heated rows and witty banter that The Avengers becomes something that I really wasn't expecting: it's really funny. All these characters are so different and come from such different backgrounds that there is a lot of fun to be had by bouncing them off each other. The fish out of water gags at Captain America's and Thor's expense are great ("Easy there Point Break") with Tony getting to roll off line after line of witty insults. And in the film's climax, Hulk gets most of the laughs as he smashes everything around him. The Hulk could easily have been the film's main weakness, Marvel had already tried bringing him to the screen twice with little success (Ang Lee's 2003 version being one of the worst superhero movies ever) but he ends up being one of the film's biggest strengths. Mark Ruffalo makes a great Bruce Banner but he actually gets to play both Banner and the Hulk through motion capture (the first time ever that an actor has played both Banner and his massive alter-ego) and it works great. There was a huge cheer and applause when Cap' got to tell him: "Hulk, SMASH!" and he proceeded to do so.
A few of the new characters and ones that were limited to cameos in previous films get their chance to shine here. Scarlett Johansson's Black Widow gets to do more kicking and is given a love interest in Jeremy Renner's unbelievably bad-ass Hawkeye. Samuel L Jackson finally gets to spend more than 5 minutes on screen after showing up in 4 Marvel movies prior to this one in part of his massive 9 picture deal with Marvel. Cobie Smulder's of How I Met Your Mother fame gets to show off her action chops as Maria Hill and the Stan Lee cameo is present of course.
Which brings us to the film's action sequences. They are astounding. Each one better than the last. An early 3 player bout where Iron Man and Captain America try to take down Thor is great, but an aerial fight between Thor and the Hulk is better. But then there's the climactic "glorious war!" which really shows the potential of bringing this group together as they get to fight as a team. The problem with them on their own as demonstrated in previous movies, is that your limited to the adversaries to give your hero. Iron Man has just been fighting other men in suits, Thor monsters, etc. But now you can throw any enemies you want at The Avengers and the action will be incredible.
The only grievance some people will have is with the villains and the Macguffin. At the beginning I thought the whole aliens and gods thing was a bit fantastical for an Iron Man, Hulk or Captain America movie, but in the end it suits the movie perfectly as the Avengers are given a main villain the can all fight with and a whole army to battle against.