The projects are really large so you'll get great experience. The benefits are good. The people are, for the most part, really nice at the lower level.
Cons
Always restructuring. You don't actually work for Avanade you work for Accenture under the name of Avanade. Accenture is always trying to absorb or downsize Avanade and even the execs don't have real power there. Plus all work and decisions are also controlled by Microsoft, so if they're doing extremely well then Avanade does and then Accenture fights for their share of the money in some shady way.