Britain's best short story writer makes an intricate, intelligent, fun and thought-provoking novel? No surprise there. I agree with another reviewer that this is solid 4-star science fiction, but that's in a world where 5 stars are reserved for the very best the genre has to offer, such as
The Stars My Destination (S.F. Masterworks)and
The Fifth Head of Cerberus (S.F. Masterworks). I rate Cowboy Angels with 5 stars because it's excellent, and it has been grossly under-rated in other reviews.
If you like science fiction, you will enjoy all of Paul McAuley's work. If you're new to Paul McAuley, his most brilliant novel, Fairyland, is easily 5-star by the aforementioned measure. Also, I'd recommend getting hold of some of his short fiction, because it truly is amazingly good. Free examples can be found on his website: http://www.omegacom.demon.co.uk. Decide for yourself, and if you like it as much as I do, I'd recommend keeping an eye out for him in Interzone.
Judging from the broad spectrum of these reviews, people either love or hate this stuff. My advice is to give him a chance and decide for yourself. Start with
Fairyland, which deservedly won the Arthur C. Clarke award.
The Quiet War (Gollancz) is another great one, as is his latest novel,
Gardens of the Sun (Gollancz). I hope you like them as much as I did.