Apparently, someone has been working to port the opensource code of Doom3 to OpenGL ES and also got it working on Android: http://omcfadde.blogspot.fi/. I am going to see if it will build at all on my Raspbian install when I get home. Has anyone else seen this or tried to get it to build?
Even if it does build/run, I doubt it will be anything more than a slideshow (seconds per frame, not frames per second) since Doom3 was very cpu heavy on x86. But its still interesting to see what the RPi can do and if the Broadcom GPU will be of any assistance.