I'm going to split this review into two parts. The first part will be for people who have not read the original graphic novels, and will be very positive. The second part will be an addendum for people who have read the graphic novels, and will begin with the word "but."
Ok, part the first. Scott Pilgrim vs The World is a comedy about teen comedies. Essentially, Scott Pilgrim is a charming geeky slacker who basically thinks the world is a movie starring himself. He dates, he slacks, he plays in a band. Soon enough he meets a girl who he really likes called Ramona Flowers, who's a new girl in town, and the two attempt to form a relationship despite the fact that she's got a lot of baggage from old relationships, and he really needs to grow up and stop being self-centred. And, if written and directed by John Hughes, it'd probably be a lot like Pretty In Pink.
However, this is that story told through the psychotically pop-culture obsessed allegorical lens of a cartoonist called Bryan Lee O'Malley, and this means that when Scott is measured up to one of her exes, that really means that he has to fight a video game style boss battle against them, her seven exes forming The League of Evil Exes. And hence, rather than a drippy film with Molly Ringwald in it, it's awesome knockabout fun. And of course, this already pretty bananas story is then passed through the psychotically pop-culture obsessed allegorical lens of the director, Edgar Wright, co-creator of Spaced and Shaun of the Dead, and hence, that lunacy is pretty much magnified. Right from the start when the movie is about to start, the Universal logo comes up, and is presented in 16 bit graphics style with accompanying 16 bit console style music.
...but. (Here comes part 2!) It's the same kind of problem I had with Sin City. When you adapt something, you have two choices essentially; get as close as you can to the original, or go your own way. And if you try to get close, anything not quite right can stick out. And what's not particularly right is the casting. Specifically, I'm afraid, Michael Sera. Now, I am no enemy of Michael Sera. I liked him in Juno, I loved him in Youth In Revolt. But he has a certain persona. He is the likeable, well meaning, nerd, meek and mild. He is the good guy. And that's how he plays Scott Pilgrim. And that's not who Scott Pilgrim is. Scott's an asshole. A likeable asshole who has been coasting on charm for too long, and needs to realise he's not a teenager anymore. That's his story, and I don't think it fits Michael Sera. So there's not really a point where I accepted him in the role.
The other thing that makes me less than thrilled is that the insanity and pop culture references are dialled down, way down. There's a bit in one of the books, for instance, where they break fourth wall, and suddenly one of the characters is talking us, the readers, through the recipe for the dinner the characters are all eating. That's gone, and no attempt is made to similarly play with the format. The original novels are meta-textually thick with references to anime, video games, pop culture, and a lot of that is cut out, which I found odd, since that's something that Edgar Wright did pretty fearlessly in Spaced (i.e. 'here's an episode that's a parody of One Flew Over The Cuckoo's Nest throughout. Didn't see it? Tough.') To see all the obscure stuff dropped for a popular movie was strangely disappointing.
Overall, though, it shouldn't matter. It's still clever, funny, insane, just how it should be.