1. On the same machine, I find VS 2012 was dragging (but memory was always hovering around 400MB)
2. Couldn't stand for .csproj style solution files (may be I'm spoiled by pom.xml, but its way better)
3. We as a team working on the same project and merging those .csproj files are literally pain in the ass.
4. The windows layout in the IDE is quite un-intuitive. You should see how IntelliJ manages all those windows.
5. The disconnected namespace and folder structure is another pain.
6. Related to the point 5, looking the source code and namespace imports, I can't see from which file those Classes are being "imported".
7. Maintaining and adding references is PITA compared to Java projects that uses maven.
Again, as I clearly mentioned, C# as language is better, but the tooling and ecosystem are not.
Its not always about the better language, Software is mostly written once, but read, refactored, maintained thousands of times by dozens of people. So the tooling and ecosystem has its place, so as the backward compatibility.