Yeah, .NET Framework was an absolute pain to work with also, there was a lot of boilerplate, especially when it came to ASP, and like you said it was tied to Windows and Windows API. Now with Core it's multiplatform and they're opening up all of the traditionally Windows-based SDKs to Core architecture and making them multi-platform while having them open source.

.NET Core is an absolute pleasure to work with, and while I'm not into Razor views, the web startup modularity and extensability of the pipeline make swapping out solutions a breeze. I can run a full React app in some a wwwroot folder that has almost 0 dependencies on the outer C# code, such that I can plug out the folder and copy it into a new directory and run it like any other React application - that was mind-numbing with ASP non-Core. I love it