Anyone play this?  I bought it on steam to play.  It's a fairly awesome game.  It started off as a mod for Unreal Tournament.

You kill zombies, and it's set in London. And is a FPS.

I was really surprised when I first played it because it wasn't the easiest game.

The game takes place in London, England. Horzine Biotech, a biotechnology company, is contracted to conduct experiments of a military nature involving mass cloning and genetic manipulation. Something goes horribly wrong during the process of the experimentations, and human subjects begin to exhibit grotesque mutations and disfigurement. They become increasingly hostile, and eventually overrun the internal security forces of the corporation.

Hours later, the first waves of the specimens break out onto the surface, disrupting a peace protest outside the well-known military contractor. Despite the best efforts of local police, the civilians are quickly overwhelmed and consumed by the seemingly endless supply of clones now streaming from the gaping maw of Horzine Biotech's headquarter. Having escaped their sterile prison, the creatures began to fan out to neighboring areas, devouring the helpless citizens of London while the Metropolitan Police bravely but fruitlessly attempt to stem the tide of mutated flesh now spreading across their city.

Desperate to contain the outbreak, the British government begins to organize ragtag teams of surviving British Army soldiers and Special Branch police officers to fight back against the hordes of mutated "specimens" now running amok throughout the capital and its outskirts. The player takes the role of an anonymous member of one of these teams as they partake in a variety of missions in and around the city of London.
http://www.killingfloorthegame.com/