It was stupid simple to get simple GUI apps up and running. More complicated apps were impossible. But, I think that's exactly what's missing in the Desktop GUI market right now. Webapps are incredibly easy to start apps with. You only need to know a few things and you can pick up the rest later as your app gets more complex. Modern desktop GUI systems are incredibly complicated, in comparison, just to open the window, let alone put text on the screen.
Later versions of Visual Studio with custom controls and other abstractions made fairly complex GUIs entirely doable and still pretty fast to build.
Then they shit canned everything for Xaml around the same time the whole industry abandoned any kind of WYSIWYG or rapid development technology.