Far Cry 3: Blood Dragon is a new standalone title which will arrive for purchase on 1st May.

Far Cry 3 - Blood Dragon cover
Details of the game have appeared on the Xbox Live Marketplace. The only multiplayer feature listed is leader boards, so it sounds like this will be a single-player campaign or maybe even some sort of challenge mode.
Here’s what the description says:
“Far Cry 3 Blood Dragon is THE Kick-Ass Cyber Shooter taking place on a bizarre open-world island crawling with evil. Welcome to an 80’s VHS vision of the future. The year is 2007 and you are Sargent Rex Colt, a Mark IV Cyber Commando who’s fighting against a cyborg army gone rogue. Your mission: get the girl, kill the baddies, and save the world. Experience every clich? of a VHS era vision of a nuclear future, where cyborgs, blood dragons, mutants, and Michael Biehn (Terminator, Aliens, Navy Seals) collide. Playing Far Cry 3 Blood Dragon doesn’t require a copy of Far Cry 3.”