Speed Racer's one of my favorite movies of the last decade. It's a great film in just about every sense. Here's why critics didn't like it, IMO:
1. It's too colorful. Fuck it, it's true.
2. They refused to take the dramatic part seriously or even pay attention to it.
The thing about the film is that there is a genuine, meaningful emotional core that gives it depth. The family drama is for real. It's written well. The acting, in scenes that actually require nuanced acting, is superb. The non-twist twist of Racer X is great, and adds a genuine bitter tang to what would have been a saccharine finale.
The messages about industry corruption and manipulation, I'm just about certain, were the filmmakers willing to bite the hand that fed them, even if it tanked their career. If anything, the film is subversive. They went and asked for a lot of money to make a popcorn film that had great visuals and was family friendly. Then turned in a movie that viciously mocks the men who held their own purse strings.
There is much more subtlety in the foundation of the film than there appears at a glance. It isn't just a cartoon world, it's a detailed alternate reality with its own history. The Wachowski's put what a lot would consider way too much work into it, so that even incidental references have some context.
And, of course, the action, staging, racing, and sheer conceptualization of the scenarios is like nothing else out there.
I do think it's a film that will curdle one's blood if they take themselves and cinema with too much pretentiousness. It's a giant piss take at a lot of things, including the Wachowski's own career and hyperbole surrounding the Matrix trilogy. (If anything, the movie almost seems like a coded personal apology from the Wachowski's for selling out, after the original Matrix, and seeing dollar signs with the sequels.)
, but really its a love it or hate it film. 
