I am a .NET dev and love the language, ecosystem, tooling and recently their open source initiatives. Few things that frustrate me. Here are my whines:

• Naming of framework — asp.net core / asp.net could have been one word say, Katana.
• Language features — I am still comfortable with C#6 or may be a few things from C#7. I know I do not have to use all new stuff, but I feel left out. Too much inertia as of now to get over the hump.
• I wanted to break into GUI stuff for long time, but there is no clear path. Avalonia is good and I hope the documentation becomes good as explained by Mike in a recent podcast.
• The company I work for has an initiative of OSP Open Source Practice. I feel bad that .NET/C# is not included in this ever. OSP only means Java, Python and probably Go. It is a nitpick, but MS has done so much to make .NET open source, yet even technology oriented companies think of MS development platform as a closed system.