With 2010, Arthur C. Clarke's ability to write interesting, believable, and likable characters has improved dramatically, particularly compared to the cardboard cutouts from Rendezvous with Rama, and the similarly bland characters (with the exception of HAL) from 2001. The book also does a great job of answering the remaining questions from the novelization of 2001.
As far as the book to the movie goes, it's something of a 50/50 split. The book is better at providing the answers then the movie is, and there are some stupid decisions that the characters make in the film which aren't made in the book (like sending Max in a manned pod out to the Monolith, instead of using an unmanned pod operated by remote). Also, the book manages to be semi-prescient by having giving China a space program that would have been somewhat unimaginable when the first film came out. However, the movie manages to be more reasonable by increasing the danger to the Leonov when Jupiter becomes a star.
All in all, 2010 is one of my favorite Arthur C. Clarke novels, and is definitely a worthy companion to 2001.