One of the greatest strengths of the film is the cinematography, which is gorgeous. The second thing that's done well is the overall tone - funny and cheerfully absurd (the material is in the text, but the actors ham it up to the max), but also dreamy and surrealistic, which is fitting. They do change the ending of the book, but honestly, I think it's kind of an improvement. They also do an interesting job on the interspersed stories. While many a director would throw on some Wayne's World diddlyoops or some kind of fade out, here it just cuts to a new story. This might be confusing to people less familiar with the text, but actually, that might be a good thing, because the multiplicity of narratives in the novel is truly dazzling, and this might be the closest the film can get to producing that effect.
The main minus is that the movie is really long. 3 hours. And it kind of drags at times, as does the book, because really, it's just a big collection of random stories. Still, it's an interesting movie, I think, and well worth watching if you can gets your hands on a copy.
*Fun fact: the movie was made in the 60s but re-released in the 90s thanks to Jerry Garcia, Martin Scorsesee and Francis Ford Coppola, who financed its restoration and distribution, apparently out of great love for the film.