If you already know what NDepend is, all you really need to know is that you can now point CppDepend at some big legacy C++ codebase and start to get your arms around all that code a bit better. If you have vaguely heard about NDepend but weren't really listening because you're a C++ programmer, it's time to change that. You can start by reading an analysis of MFC that uses CppDepend to answer questions like what fraction of member variables have names that start m_ (answer: about half) or what kind of coupling the key classes tend to live with.
Beatiful visualizations and genuine insight. Sure, you're not going to refactor MFC yourself, but imagine pointing all this at your own library!