Based on the EDuke32 game engine, NBlood is a new open source port of the classic FPS Blood. From what Voidpoint (Ion Maiden) said on Twitter, it's using their version of the game engine too.
OpenMW, the excellent open source game engine for Morrowind has made some interesting progress towards supporting later games like Oblivion, Skyrim, Fallout 3 and New Vegas.
The people over at Unity have put out the first beta for the first major release of the year and there's tons of new and improved bits for game devs and Linux gamers.
Keeping tabs on various open source projects, one I'm quite keen to see progress further is the KKnD and KKnD2 remake. They just recently pushed out a new build to improve it further.