My sentiment is best summarized by this reviewer:
Speed Racer may very well give your brain diabetes, and I state that as compliment.
The plot is pretty predictable (evil megalomaniac with henchmen, unlikely alliance of good guys, various plot twists) but fairly well done, and the characters are enjoyable to watch.
The visuals, however, are stunning. From the studio logos all the way through the closing credits, Speed Racer contains contains gratuitous amounts of color and motion. It's gripping and fluid and, yes, beautiful. The Wachowskis have apparently figured out exactly how to turn on the pleasure centers in human brains, which is pretty remarkable. What more could you ask for from a movie?