I like the perspective of the Bobs, and how this basically handles the idea of a Von Neumann machine in a fresh (to me) way. The idea itself is not new, remotely, but the way it is personalized is fantastic. I read something else from the perspective of a Von Neumann machine a number of years ago; can't remember what it was, but it didn't have the same personality. I think... maybe it was Spin, by I forget the author. Basically the earth gets wrapped up in a giant shell for a number of years, and the premise of that is really cool.
Anyway, yes, the chief antagonists here aren't that novel, but the way they are handled has me interested. The way the combat plays out so differently every time, it also never feels stale, which is really good. The anthropology aspect is also interesting. Plus all the general geek references.