The score as a whole is boring and, as CC says, simplistic attempting to be complex. Still, there a some passages that are gorgeous, particularly the first minutes of Paradox and most of Time. These, plus Mombasa, are the scores best tracks.
The rest sounds a little too oppresive to be enjoyed, although "Dream is Collapsing" does sound quite exciting within the movie.
Zimmer uses some sound resources that make you feel as if the music is part of a dream and it is suddenly interrupted when you wake up, which, honestly, is a bit cruel when done on the album. Why not make the music itself sound as in a dream?
Still, the music works in the movie and the album does have some standout cues, even if they are highly similar to the composer's previous works. As a whole, the score for Inception is by far superior to The Dark Knight and other lame Nolan films' scores, but it isn't among Zimmer's best efforts. 3/5 stars from me.