If you wanted to bring up an example of how modding can lead to big things, most people would default to Counter-Strike. The Half-Life mod got so huge that it spawned a stand-alone title and became a fixture at the casual and esports competitive level for several years. Those who are more concerned with co-op play would point to Killing Floor as another success story. Starting out as an Unreal Tournament 2004 mod in 2005, it also gained enough popularity to warrant an improved standalone release in 2009, and it continues to command an audience to this day. A sequel is finally on its way, and we came away extremely impressed with the Early Access version of Killing Floor 2.

Despite the large amount of time that has passed between releases, the story takes place roughly a month after the outbreak in England. With things still out of control, the zeds have made it to mainland Europe, where groups of survivors have banded together to stop the menace one location at a time. If anything else, it gives the game an excuse to visit a wider variety of European locales.

The core game remains the same. With a total of up to six players, you pick a class and enter the battlefield. The match is set in rounds, where each round has a specific number of zeds that need to be eliminated. Once you do that, you head over to the trading outpost to refill your supplies and get better weapons, if you can afford it. After a set amount of time, the trading outpost closes, and you have to face another wave of even stronger zeds. This continues until the final round, where you go against a much stronger patriarch zed.

There are a few changes to the otherwise familiar formula. Outposts are now in pod form, so the room isn't locked once a new round starts. The doors can be welded shut, but once the welding seal breaks, the doors go along with it, so the entrance is open for the remainder of the match.

Characters can run, giving them some speed even if they're heavy with the weapons they're carrying. All of the classes you pick start off with a pretty healthy set of weapons. Everyone still has pistols, knives and a personal healing needle, and now, your characters also start with better guns and melee weapons, depending on their class. There seems to be no real disadvantages to picking up and using weaponry designated for a different class. Unlike the first game, where using a weapon out of your class meant poorly controlling it and wasting ammo, everyone can use any weapon. Matching them with the appropriate class simply wields small bonuses. Finally, the class leveling isn't much of a grind anymore, since every task (instead of specific tasks) boosts your XP. Reaching the max of 25 still takes some work, but at least it conforms to your play style.

The Early Access build is fairly limited in scope. There's only one mode so far. which is the aforementioned Survival mode. The map selection is limited to three, so all of your fights take place in either an abandoned underground science lab, a research center on a snowy mountaintop, or a torn-up section of Paris. There are only four classes to choose from out of a proposed 10 for the final build. The Berserker has a firearm in the form of the nailgun but is much better with melee weaponry, especially since the class can parry nearby zeds to push them back. The Commando is all about firearms from a safe distance, as opposed to the Support class, who gets firearm action at a closer distance with its shotguns. Finally, there's the Field Medic, who has to balance healing teammates and harming zeds since both of those bullet types come from the same ammo pool.

Even with those limitations in place, Killing Floor 2 has more than enough content to provide a great deal of fun. The maps are well designed to be multi-level affairs that flow into some sizeable areas, and there aren't any dead ends. There are bottlenecks, though, and the wide-open areas mean that zeds can appear from all sides. Roles are clearly defined by their weaponry, and while communication is wildly helpful, you can get past a level with a bunch of competent random players who know their job well. That balancing is crucial, since the game does a good job of ramping up the difficulty rather quickly. The first round of a match may see you going up against normal zeds, but the second throws in ones with active camouflage, sword hands, leapers who walk on four limbs, and larger zeds, just to name a few. With screamers, chainsaw wielders and fireball-throwing ones later, the only way to survive is to ensure that your team is comprised of every possible class.

The only issue thus far is the same one that plagued the first game: the survivability of the solo player. Though the game is meant for multiplayer play, there is the option for solo play that's been scaled down accordingly. Even then, the game has no quarter for those going at it alone and sends enough high-level zeds by the second round to serve as an extreme form of practice for players before they go online. The zeds all have a tendency to form tight crowds around you and, backing into a wall or corner is a quick way to deplete your armor and drain your health. The global nature of XP means solo efforts aren't in vain, since that eventually carries over to the class leveling. If you're starting the game fresh, playing solo simply invites frustration, unless you really love tackling a near-impossible challenge.

As expected, the passage of time between games means a big jump in presentation. The metal music is there but is quickly drowned out by some loud gunfire and zed grunts, so you'll almost forget it exists — until you see a song title appear in the corner of the screen. The game takes that engine leap from Unreal Engine 2 to 3, and it shows some spectacular environments and redesigned zeds. The frame rate is also rather smooth, and the title's ability to handle lots of on-screen zeds at the same time is great, especially when you see the aftermath splattered in the environment. For those worried about the graphical leap requiring a hefty amount of horsepower, the recommended specs are low enough that any PC built in the last few years can handle it. This ensures that the player population will stick around for quite some time.

Killing Floor 2 might be more of the same on paper, but that's just what fans are seeking. Even in its current state with the small amount of available classes and levels, the action is intense, and the difficulty never lets up, even if you have the most balanced team out there. The game is currently available on Steam Early Access, and for fans of pure multiplayer co-op mayhem, it's worth checking out right now.