I've never read the books, loved the mini-series, and enjoyed the movie. Yes it's different (very different in some respects), but hell, I already have the mini-series, so it's no big deal.
What struck me the most was the difference in the ending:
Spoiler
Sticking in a happy ending definately threw me at first, Arthur gets the girl, and doesn't get stuck on primal Earth with Ford, but again, I have the mini-series for that. Hell, I thinkt he one thing I missed the most from the BBC version was the design of Deep Thought, while interesting, the new design didn't do it for me.
And hey, didn't everyone like the cameo of the original Marvin suit? I half expected him to start talking.