It does, and it doesn't. It is a little more close to the first novel than the first four radio or tv episodes. But there are quite a number of differences. I think for the most part it did work out well, though there were some bits I missed having, like the confrontation with the Galactic Police in Radio/TV Episode 4, or the end of the first book. In the movie it's a confrontation with the Vogons. Not that there's anything wrong with that, it's just that that particular scene has its own odd bit of humor, and it got cut. There's also the confrontation with Eddie the Shipboard Computer's "Emergency Backup Personality" when they first land on Magrathea that's completely missing. A lot of the new stuff did fit rather well, I thought, and left several plot threads open for a sequel.

Oh and yes, 3 of us went in robes, and a total of 4 of us had towels (and we weren't the only ones with towels, though nobody else did robes ). We got cut down to six from eight when my younger brother and his friend backed out - they decided to go with their circle of friends and do something else....