Just got back from it. It's probably one of the most colorful films I've seen yet coming out of a digital projector. So unless you're one of those whose parents were raped by a rainbow when you were a kid, there are skies so blue in this film it will make your eyes bleed. It really does succeed as a living cartoon. The moment the film starts it feels like someone just handed you a fruity candy cane laced with acid.
I never was into the show when I was a kid but as I got older I could appreciate the sheer cheesiness of its style. I do think that the Wachowski's accomplished what they had set out to do, which was take the tone of the cartoon and exaggerate it for the big screen. The races were very kinetic, my favorite being the one that plays out like a "Wacky Races" cartoon with weapons and car-fu. Plus it's got ninjas and John Goodman, and they're always intimidating badasses (well at least Goodman is).
I did have some problems with the film. I felt the first half was a bit weak and Speed came off as a shallow character. It also had some pretty poor pacing issues. There were moments where I got confused by what was a flashback/flashforward and what was present time, and I also felt the film went one race too long (there was a moment where it looked like it was building up to an ending but instead went to another race). I also think the film had an unnecessarily complex story dealing with corporate greed and corruption. One that is surely to fly over the majority of children's heads.
The movie does have a couple of distinguished mentally-challenged kids' moments. You know, those moments of sheer brain dead stupidity that have plagued children's films since the 90's. Thankfully those are few and John Goodman was always around the corner to balance things out. Speaking of which, Goodman easily overshadows everyone else in this movie. His character probably has more depth and emotion than the entire cast combined.
Overall I think Speed Racer falls into the "good but not great" category. It's definitely got more energy and imagination than Iron Man did, and does all it needs to do in one movie without cockteasing at a potentially better sequel.