NDepend is an effective tool for analyzing .Net assemblies and provides information so that you can have an idea of whats going on. There are use cases for this in our development cycles. For the purposes of simplicity I'm going to show the usage based on analyzing NAsserter.
I recently posted some code to Google Code called NAsserter. NAsserter started off as a proof of concept for prototyping something I had been able to do within Unit Tests (being able to make fluent style assertions in code) except for the purpose of throwing exceptions in code. This is the first fluent API I have written.
The API for NAsserter started as a small simple class and grew bit by bit. I tried to refactor as much as it made sense to me. I didn't model my internal constructs after any other fluent library as most of them have a need for much more extensibility than this. The biggest inspirations were NUnitEx, NUnit's constraint based model and Fluent Validation. These three projects provide exactly what they aim to, in which NAsserter is not intended to overlap. NAsserter is NOT a Unit Testing or Validation framework. It's simply for throwing exceptions in a predictable manner, including the messages. Thanks to Tuna (NHibernate & Castle contributor) constructive feedback.
Upon getting a version of NAsserter (0.1) released that I am comfortable with, I proceeded to analyze it with NDepend; which I am still learning.
One of my favorite sections of the report is the assembly metrics which shows how abstract, stable, complex and well commented the code is. I think the metrics of what you are looking for may be a little different based on if you are developing a framework (even the type of framework) or enterprise systems. For instance, often times frameworks developers will make compromises in design for simplicity of use which is pragmatic: use common sense.
NAsserter is a simple codebase which shows through the analysis (the only dependency is mscorlib the .Net CLR) and doesn't really do NDepend justice. NDepend is nice on large projects with a number of dependencies, especially for keeping track of different design metrics. I am still learning the tool myself and I am finding new uses for it continually. You can track your project's progress on different metrics since it keeps a baseline of the metrics. NDepend is also very helpful for code reviews to be able to have an objective analysis of code, reducing some of the human element.