Assuming CORE ever comes out, it has the potential to be good. It looks Quake-like with some fast paced action. It was supposed to be out the 14th of this month, but now it's May 12th along with Black Sigil.
C.O.R.E. video:
And for now, there is another unusual choice that people usually pass up- Bionicle Heroes. It is a surprisingly fun, engaging, and attractive FPS. It was overlooked sadly due to the name. No one imagined that there could be a decent game based off Lego Bionicle. Try it out. I'm not usually into FPS (besides Metroid Prime), but I liked this one.
Here's a video of Bionicle Heroes DS: