Great if you're an engineer, not so great if you're in UX or not in Mountain View
Pros
Lots of freedom, cool projects and great colleagues. You have to find the right project though, where the team does appreciate UX as that's not always the case. Manage that and you'll have a blast. Also great benefits (good pension, medical insurance plus things like gym membership, and of course free food) and a very decent salary.
Cons
Google doesn't really seem to understand UX. Design decisions are often made by committee and based on technology or what the VP likes. The UX designer then gets the job of painting the pixels. There's also little understanding of the different roles within UX (visual designer, interaction designer, researcher). I find the work very simple and repetitive do miss the more interesting bits of UX design (conceptual, strategical work)