Okay, I think I've calmed down enough now to make a coherent(ish) post about this wonderful ball of amazingness. XD Although I've got to get a few things off my chest first.
1) Everyone and their dog/cat is going on about how amazeballs this film is. And it is. But, with certain pre-conditions. If you don't enjoy the superhero genre or are expecting a LOTR style epic masterpiece thingy then you'll be disappointed. It's a great superhero film, really enjoyable, got a lot of heart but don't expect something Oscar worthy. ^_^
2) While you can enjoy this film without having seen the Marvel films before it, I wouldn't recommend it. A big part of the appeal of this film was the character interaction/development and Joss did great work building on top of what had come before instead of just starting from scratch. There were moments in the film for Cap, Thor and Iron Man that hold more meaning if you've seen the other films. Out of all of them, I'd say Thor and Cap's films are the most important to see before going, but Iron Man's films are great too.
3) The Avengers is not Batman. XD A lot of people have been comparing the two lately, but to be honest, the only thing they have in common is that they're both based on comic books. Avengers is a straight up comic book film, and I love the Nolan Batman films but I'd be hard pressed to call them superhero films. It's more like, if Batman existed in real life, this is how he'd be.
Now, with that out of the way, review time! I loved, loved, loved this film. I could seriously watch this every week until it left the cinema, but then I'd be broke and this film already has enough money. I feel like it was completely enjoying being a superhero film, not worrying about whether non-comic book fans would find certain things weird or silly, and it just went and had fun. A big part of this is because Joss is a fan and knows the genre so well and he just brought it on this. If he doesn't do Avengers 2, I will be so damn upset.( Spoilers with gifs! )
One of the great things about this film is the hilarious/cute fanart that has come out of it.( Spoilers!! )
Please take note Hollywood. Things don't have to be doom and gloom in order to make bank.