"It doesn't matter if racing never changes. What matters is if we let racing change us."
I thought Speed Racer was a pretty good adaptation of the manga and anime. Visually, it was astounding. In HD, the colors are incredibly bright and vivid, and the constant special effects really helped to bring the world to life. I imagine people who watched Tron for the first time back in the 80's might have had a similar reaction to what I had watching this. All the various camera techniques used to make it look similar to the comic books worked well, and I just really liked the style of the whole thing. I don't think I've ever used this phrase before, but it really was a feast for the eyes.
As for the rest of the movie, I also liked the cast. Emilie Hirsch might not have immediately jumped into my mind as the ideal Speed, but he worked. So did the actors playing the rest of his family and acquaintences (both helpful and adversarial), and Christina Ricci as Trixie. It took a while for Matthew Fox to grow on me as Racer X, but by the end I had to admit that he wasn't a bad choice, either.
The story was a combination of some original material and a bunch of new stuff that the Wachowski's came up with, and it made for a fun, if conventional, plot. The races were suitably thrilling, there were several funny scenes (what could have been an annoying role by Paulie Litt as Speed's younger brother, actually ended up being quite humorous), and I had a smile on my face more often than not. That's the recipe for an enjoyable movie, in my opinion. Try it if the source material interest you, or you'd just like to watch a fun movie full of eye candy.