I'll second this suggestion. In my experience so far, webapp2 is a great way to get beyond some of the stranger idiosyncrasies of the default webapp without being overwhelmed or completely throwing away the benefits of Google's extensive documentation. If you like an extension or modified feature, use it. If not, do the way Google tells you to and it'll work just fine.

If you use nothing else, the extended routing functionality and lazy loading of handlers are big improvements and are pretty painless to implement.