Shaders seem all the rage these days. Now Thunder n Lightening has support for them too just days after Danger from the Deep implemented shader support. Wavey reflecty shiney water. I smell pretty FOSS games! :-)
Actually the first FOSS game I remember getting such fancy effects was Boson. A 3D RTS, the codebase suffers from KDE dependencies which limit portability somewhat as well as making it a pain to install on Linux systems without KDE. Given how cool it looks, I'm sure they'd be much further on as a community if it was easier to install on non-KDE systems. I'm sure they would get much more developer interest if the game were available for Windows and Mac OS X and available in a format other than tarball for Linux.
Somebody just pointed me in the direction of Qonk, a space strategy game. It's in the early stages of development but has a much smaller scope than typical space strategy projects like FreeOrion, so is already very playable. Games only last a few minutes, and it is billed as, "a small build-and-conquer strategy game with very simple rules."
Finally, Bygfoot 2.2.0 was released mid-May. Strangely it didn't appear on the Game Tome or Freshmeat. It seems that new developers have taken on the mantle of improving this FOSS football management game, which can be downloaded for Windows and popular flavours of Linux and probably compiled on Mac and BSD systems. This is the only well-featured open source football management game going although personally I find the UI to be counter-intuitive. Other than that I found it a lot of fun when I played it last year so it can only be better now.
As a recovering Championship Manager addict (that game destroyed my teenage years) I'll probably not try too hard to get into Bygfoot. ;-)