I am almost always disappointed by collaborations. I can't recall more than one other favourite book that has two authors, both respected in their own right.
The work is thought provoking, engrossing and essential reading, in my opinion, for those who like science fiction. One of the benchmarks for science fiction is to create a truly alien alien, and this hits that mark.
It also has cover endorsements from Robert Heinlein, Frank Herbert and Theodore Sturgeon, but lacks a comparison with Dune or Lord of the Rings :-)