I don't think WPF is a replacement for Winforms. But WPF is a more advanced framework for creating windows based applications. Lot of developer use to think that, it is just create application with good look and feel, with animation like flash. But WPF is more than that. The framework itself very different than Winforms.
First thing is, Winforms uses User32 and GDI32 dlls extensively to work. But WPF is not using GDI32 at all. But it does very minimal usage of User32.
WPF has more advance rendering system where all controls will be vector based rendering. So, the control will be looking with same clarity even if the resolution changes. But that is not the case in Winforms because they are using GDI32, which will not do automatic scaling. If you use the same application in higher resolution, that will be displayed in pixels.
Another cool thing is separating code behind from design. Which will help the developers to concentrate on coding and the designers to concentrate on design. Even though, XAML is the language used to design WPF application by default, we can do WPF applications without even XAML.
Next feature is, Writing 3D application and making wonderful graphics are very powerful in WPF because, WPF frameworks will be able to directly talk to DirectX through the unmanaged layer called Media Integration Layer(MIL). Also, WPF make use of 3D rendering pipe line to render everything on the screen so, that make the WPF possible to create very powerful graphics application
WPF has very powerful Data Binding concepts using Dependency object. Also, WPF has advanced concepts for Text and Documents layout.
Apart from all of the above points, another good reason, why you may want to use WPF is, Microsoft is extensively using WPF for Visual Studio and other things. With the latest Visual Studio Editors, we can do zoom and other functionalities, just because of WPF.
Even though Winforms are very successful for the past 15 to 20 years may be more, we have new frame with advanced concepts to support all new hardware changes we see in the recent days also, its better to move ahead with the new technologies and stay on top. Since we have no other new framework for windows except WPF, I would suggest go with that until something new comes.
Note: WPF has very big learning curve to make the application successful. Otherwise, you will see lot of performance and other issues
