(Maven) m2clipse alone is a very good reason to learn Eclipse.
You can't download 3rd-party library with Documentation _and_ Source Code _and_ Navigate to the code without having to setup anything _and_ included in your build like you would have in.NET.
It's a big plus for incorporating and debugging code when you need to do so.
I've done C# and now fully Java (and JavaScript) and I wouldn't go back to a more locked and dumbed-down ecosystem.
C# the language may well be better than Java but that alone is not enough of productivity boost.
Eclipse, Maven, FindBugs, CheckStyle, Jenkins, Tomcat, Jetty, rich 3rd-party ecosystems are the key of my productivity boost.
VS.NET, NuGET and having to write either MSBuild or NAnt plus IIS (express or not) aren't cut it. Not enough to be agile.