So far the time I have spent working with Mezzanine has been great. The code is very well written and understandable making it easy to dive in and make fixes and/or changes to suit your needs. Using Mezzanine's page_processors it is also very easy to add custom logic to any page you have created without having to modify the core codebase. The community around it is also great and very responsive, helpful and open to make changes to suit the needs of users.

Mezzanine provides all the basic features you would need in a CMS and then makes it very easy to add anything custom or unusual you might want. In this way you don't get overwhelmed by stuff you don't need.