Every iteration of the series -- the original BBC Radio series (by far the best), the books, the BBC TV series, the vinyl LPs, the audio books (abridged, read by Stephen Moore (Marvin) and unabridged, read by Adams himself), the CDs, the third and fourth BBC Radio series -- has been different from each other, some in minor ways, some major. The movie was a sad but semi-effective compromise and, if looked at strictly as "the Movie Version" in a collection of alternate versions it's passable. A huge disappointment but better than no movie at all. Or maybe not.
The whole frolicking dolphin opening credit sequence preceeding the traditional HHG opening reeked of studio interference and was the most offensive, out-of-place part of the whole thing. Douglas Adams would have farted with bemused displeasure.