To my surprise, what I got was a pretty much family-friendly film with humor (most of which I was able to watch without wincing too much, which is not commonly the case), tons of (properly) anime imagery and in-jokes, and properly OTT villains and action. The plot is pretty straightforward -- you can predict most events with ease -- but then, the source material isn't exactly Byzantine in structure either. The acting is surprisingly good; without it, the movie wouldn't work at all, given its hackneyed nature.
It DOES have some wince-worthy moments (I really wish they could have eliminated the Annoying Younger Brother and the Monkey, but alas, those are key elements of the original), and as one poster on r.a.a.m said, "there are colors here which are NOT found in the rainbow (patented ILM). There were times one wanted very dark glasses.
The racing is very much over-the-top too, but that's deliberate, and I think well-done. They do in my opinion an EXCELLENT job of weaving backstory into current events. I never saw more than an episode or two of the original, and almost nothing of "Whacky Races" which is also incorporated in a number of references. The world of Speed Racer, here, is an odd alternative history where car racing became THE big thing of the future, eclipsing all other sports. It works, within its narrow confines. The pacing is excellent from my POV and it ends well. The kids will love it, I think.
So overall, good job! And now I won't have something to hold over Kathleen's head for the next ten years.