WPF is, by far, the most pleasant and flexible thick client, windowing system out there. XAML is a bit verbose, but the binding capabilities combined with an open source MVVM framework like Caliburn allow you to build extremely flexible UIs.

WPF also abstracts control behavior away from presentation and allows you to easily and quickly extend the base set of controls to do whatever you want to.

After building multiple thick client applications using VB6, MFC, Swign, Winforms and WPF, WPF exceeds all of these, by far, in flexibility and maintainability.