Got some more details! I had a chance to check it out first hand.
It comes with 5 maps:
Biotics Lab
Farm
Manor
Offices
West London
The game is standalone now, but you can very clearly that it is a UT2004 mod. The screenshots are, quite frankly, too good. The model design is not bad, the textures are great, they've added some filtering effects but the overall look is very dated. A lot of the videos I've seen on YouTube (i.e. Killing Floor Trailers) are unclear and are filtered, pretty deceptive. Anyway, just keep in mind that the visuals are not quite as good as they're made out to be.
Gameplay-wise it's pretty basic.You get to choose your appearance from 1 of 6 available in each map. If you had racked up enough points you can purchase a specialty or "perk" at the character select (or at the trader between waves). The game is basically a variant of the Monster Hunt game type from UT and UT2004. Zombies/monsters come at you in successive waves, giving you a 1 min break in between waves to prepare and restock. The difference is that there's a trader shop, where you can buy new weapons and perks, whose location changes with each wave forcing you to rotate around the map until the match is done.
Six player coop is alright, though it can get a little crowded at times. The format of the gameplay encourages players to cooperate i.e. one guy will restock on medpacks while another guy welds the door shut, another guy could focus on heavy gunning while another on sniper-savvy weaponry. Basically no one can survive on his own because you can't have it all. The sniper is too slow to handle hordes and the heavy gunner is too slow run around, a medic may favour carrying more medpacks over the weight of an armour vest, etc.
It's an interesting idea but I honestly feel it would have had way more success had it been a mod of L4D! Adjusting and building on the L4D formula would have allowed these guys to focus on the gameplay, which is supposed to be KF's primary offering.
With the final SDK nearly at the door I think it's plausible that someone will make a mod for L4D that'll basically undercut KF.