The UI part is exactly what I meant. WinForms was a godsend for professional developers making line-of-business apps, because previously if you used first-party dev tooling, you either had to deal with the considerable limitations of Visual Basic, or you had to deal with MFC that was low-level enough that all the things that were tedious about Win32 remained tedious. In comparison, Borland had Delphi, and there was a good reason why it was so popular back in 90s and early 00s, and why Microsoft ultimately acqui-hired its main designer specifically to work on .NET (and it very much shows in the design of both C#, which owes as much to Component Pascal as to Java, and of WinForms, which is so similar to VCL).

With WinForms, we actually got something that was convenient without shackling you. And the whole cross-language story was great, too, especially around .NET 2.0 - with C++/CLI you could very easily wrap any random native code C or C++ library for consumption from .NET, with end-to-end integration in the build system, IDE etc.