First-class Immediate Mode Graphics Support (Direct2D)
WPF's retained-mode graphics system is great for controls and is probably all you need if you are developing database forms applications. But there are classes of applications, particularly data-driven visualization apps, for which the overhead of retained mode makes it unusable. The current alternative of using WriteableBitmap is an okay workaround, but there are still many challenges, such as synchronizing your bitmap updates with WPF's rendering cycle. WPF v.next should be canning support for XP, so it can move to DX10 and so be on par with Direct2D/DirectWrite. WPF with first class support for immediate-mode graphics via D2D/DWrite will simply be unstoppable!