As someone who's worked on a moderately large Django project, I have to disagree. There's a lot of stuff done for you without you seeing it (like Admin and the default QuerySets + Managers) but it's fairly easy to understand, customize or debug if you want to and Django's source code is actually really readable.

Plus, Django has some of the best software documentation I've ever seen. It was incredibly rare that I couldn't find an answer to how/why something worked in the docs.