It may seem like we already have tons of excellent modern FPS's out there right now, but the potential FPS game of the year is coming soon...
Beta info:
http://xbox360.ign.com/articles/859/859204p1.html
In short: You must be an IGN Insider member and have an XBL Gold membership to receive a beta key. The beta starts March 25th and is for Xbox 360 only.
EDIT: You can also get the beta key with a preorder at Gamestop...
http://www.gamestop.com/gs/swoffers/default.asp