I've never seen a qualified response to this question.
.NET is by Microsoft. It's Windows based. It's been around for a long time. It didn't introduce any new paradigms, and I'm guessing isn't used by a single startup in California.
But it's fast, it's solid, and from my experience, there are more well paying, reliable opportunities in it than with any other language.
Honestly, I'd rather be spending my time learning Node or Ruby or heck even sharpening my PHP skills. But I enjoy .NET and would much rather work at the company I'm currently at, in a position I like with people I respect, than jump ship just for a non .NET opportunity.