Killing Floor 2 is a first-person shooter (FPS) released in 2015, and Tripwire Interactive shows how much they've improved since the first game's humble origins as a mod for Unreal Tournament 2004. In this co-operative zombie apocalypse game, up to six players are tossed into various maps and tasked with killing wave upon wave of zombies, eventually culminating in a boss fight. Killing Floor’s zombie apocalypse is powered by clones that have broken out of Horzine Labs, rather than re-animated corpses, but the end result is much the same as other zombie apocalypse shooters - the Zeds have taken over Europe, and it’s up to the mercenaries of the Horzine Security Division to contain the bloody mess.

That blood has to come from somewhere though, and the game supplies plenty of fresh meat for that. The enemy types are quite varied. You have your common shamblers, fast and aggressive berserkers, disruptive Zeds that can break up player formations, the miniboss zeds, and even a few robots thrown in for good measure. The dozen or so Zed types, while individually simple in nature, create wonderfully emergent patterns of gameplay as they start to group up. It’s a design approach that has proven itself time and again, and it works just as well here. When Zeds are coming in thick and fast, it becomes a panicked scramble as players try to correctly prioritise targets, distract miniboss Zeds, and stop the disruption all at the same time.

To add to the Zed menace, the graphics are pushed to the limits of Unreal Engine 3. This tech may be two generations out of date by now, but you probably won’t care much for the difference. Environments look well and truly desolate and abandoned, with props and furniture tossed about. The lighting and shadows in particular hold up reasonably well, providing plenty of dark spaces and blind spots for Zeds to sneak up on players, especially as the lights are destroyed by all the gunfire. The roars of mini bosses have an appropriately intimidating quality to them, which makes for a curious counterpoint to the adrenaline-pumping metal soundtrack.

Amidst all the bloodshed, you’ll occasionally trigger the game’s much-touted Zed Time, where time slows to a crawl for a short period. Most of the color is drained, leaving players with a black and white and red view that accentuates the blood spray. Games start with pristine and unbloodied maps, but as Zeds die, their blood permanently stains the map, creating a literal killing floor. If you ever wanted to see heads and body parts explode and dismember in slow motion like those YouTube videos, this game has plenty of that visual spectacle.

In the fight against the Zed army, players have ten different perks to choose from; these are the classes of the game. Perks are wide ranging, and they all play quite differently. Relatively standard perks such as the assault rifle-wielding Commando, the sharp-eyed Sharpshooter, the healing Medic, and the shotgun-toting Support, are here as you might expect. Killing Floor 2 is not satisfied with these stock-standard distinctions though, and offers various perks to fill in gaps. Want to set the world on fire? Play a Firebug. Want to play a short-ranged sniper? Dual wield your pistols as a Gunslinger. Do assault rifles not have enough bullets for you? Hose everything down with sub-machine guns as the SWAT. Want to get up close and personal? Swing your blade around as the Berserker. Not sure what you want to do? Play the jack-of-trades Survivalist. There’s a wide variety here, and as you level up your perks by playing, you’ll also unlock new skills to further customise your playstyle.

A large variety of weapons are at your disposal for taking on the Zed army. As players rack up kills, dosh is awarded and used to purchase better equipment between rounds. A majority of firearms are modelled after real-world counterparts, but there are also plenty of improvised or exotic weapons. Beyond the standard small arms and military explosives, players also optins for freezing enemies, setting Zeds on fire, disrupting, and confusing. The melee combat is also highly satisfying on a level that no FPS gamer has the right to expect. If you're a veteran of the original Killing Floor, know that a lot of mechanics you know and love had to be changed to make way for the vastly improved melee. Of particular interest in regards to equipment is that every player gets a recharging medical syringe, and there are weapons of each major type with a healing dart function. It’s a wonderful design that allows even the most flagrantly lone wolf player to play the healing game without sacrificing offense, and other class-based shooters could probably learn something from this approach.

If it isn’t obvious already, Killing Floor 2 has plenty of violently objectionable moral content. The previously mentioned Zed Time mechanic takes the excessive violence and slows down the gory bits. The game is not satisfied with simply showing the violence, but goes to great lengths in glorifying the mass mutilation as blood sprays all over the place. There is an option to minimise the gore, but headshots will still visibly pop Zed heads, so I can’t in good faith return the single point afforded by our reviewing standard.

Multiple characters in game use foul language in their voiceover lines. Every single word listed in the aforementioned rubric is represented here: fart, poop, pee, H*ll, sucks, crap, a**, b***h, b**t**d, s**t, F-word. God’s name is used in vain (“God almighty, it stinks in here!”), and at least two of the characters make constant sexual references. All characters are dressed entirely appropriately for a battlefield, although Zeds don’t follow that rule. While the basic Clot shamblers are nude, there’s really nothing sexual about them. Sirens are so emaciated that they’re more discomforting than provocative. Only the Stalkers have a figure of any allure, although the model has no more detail than you would get from a Barbie doll. Occult references are found on a few maps, such as candles and summoning circles, but for the most part it’s there for the cultic horror imagery rather than to imply the supernatural.

Finally, a few characters are motivated primarily by wealth, and the game’s thematics tie into this. Players earn literal piles of money at the end of each mission, and viewing your personal vault eventually becomes a visual spectacle unto itself. On that note, there is a loot crate system in place. While all loot crate drops are cosmetics, a small number of players may potentially find themselves overspending on keys to open these crates.

Killing Floor 2 is good fun if you have no qualms about painting everything red amidst a bevy of profanity. The gunplay and Zed Time are highly satisfying to primal urges for violence, while the emergent gameplay of the various Zed specimens will engage the strategic players. It also has a six-player limit where most games of this sort would stop at four. If you're a veteran of the original Killing Floor, this sequel is an overall improvement, not just an expansion pack. But whatever your previous experiences, just be careful not to slip on all the blood.