umm... I've programmed in VB6, Java, C++, and .NET (VB.Net for work and C# for my hobby projects). No one here has seen the CF code (besides the programmer) so we can't really judge how well it's programmed. Not to slam the guy that wrote it, but I'm just saying. You never know. I've never had speed problems with my .NET apps. Like xBrady said already, to say that .NET is slow because CF is slow is a bit of a jump.
BTW, here's Quake II .NET: http://www.vertigosoftware.com/Quake2.htm
and here's Quake II Java: http://www.bytonic.de/html/jake2.html
If they can do that in .NET and Java, I'm sure you can make a very fast front end.