Although the core libraries in .NET are huge, many are also very shoddy. There are also a few great API's, but the overall quality and usability is pretty uneven. This is mostly a problem with API's back from version 1.0 - however, unfortunately, those API's often haven't been updated. Documentation is also not always equally good; MSDN has lots of pages that describe a method Bar.Foo() as "Fooing a Bar", which is next to useless. I get the impression the java APIs are often better documented.

NuGet might really turn things around; here's to hoping...