A lot happens in the book and it explores a large number of interesting ideas. Sure it is long, but every part fits well together. As a result the universe feels more fleshed out and cohesive than the Culture books, and this is something I look for in sci-fi.
I've read every Culture book twice, and don't really have any desire to read them again, at least not for quite a while. The Algebrist I've read four times now and each re-reading finds something new.
What would you cut?