It used to be VB.net and other such stuff. It WAS pretty terrible. Ive had to pick apart some pretty horrendous applications. Then Mono/C# popped up and a lot of community effort went into making everything better. It helps that .net stole a LOT of functionality from Rails/Django/etc... and make it much easier for devs to do actual work on it.
The problem is when we talk about .net it could be a huge combo of tech from the last 10+ years. The newest iteration is fine. Its fast at least with C#.