Republished on Wednesday, 31st May 2017: We're bringing this review back from the archives following the announcement of June 2017's PlayStation Plus lineup. The original text follows.

It's been a demanding shooter season so far. DICE hit rewind on history and gave us the uniformly proficient Battlefield 1 then Respawn followed with a superior sequel in Titanfall 2. As if that wasn't enough, Activision hit us with the one-two punch of a new Call of Duty and a revamp of arguably the best title in the perennial shooter series, bundled with full online suites for both games. Amid all these blockbuster campaigns and addictive-by-design multiplayer modes, it would be easy to miss something like Killing Floor 2 – a sequel to a PC-only indie title that, for all intents and purposes, looks like a Left 4 Dead clone. Arriving at a time when CoD zombies has pretty much dominated that particular sub-genre, why should you factor this into your colossal pre-Christmas purchases?

Anyone who's ever played a co-op FPS before will be familiar with the basic flow of Killing Floor. Players attempt to survive ten waves of randomly spawning enemies of various types. After each round, any money earned can be spent at one of a number of hubs scattered across the level; here ammo, armour, and weapons can be bought or sold before the next wave. So far, so familiar.

Where the game varies things up is with its perks: a class-based progression system that's as open-ended as it is surprisingly deep. Each perk represents a class, with specific starter weapons and gear. Using the weaponry of that perk, or performing certain actions tied to it, will level it up. Each levelled tier offers a choice of two boosts, so it's tempting to focus on a particular class to unlock its strengths, but how you decide to do that is enjoyably freeform. All weapon types are available to buy at the level hubs and, taking into account inventory weight limitations, can be mixed and matched to progress several perks at once. Likewise, the actions tied to them are versatile and extend to others, so a healer can use a SWAT weapon for a short spell and progress both perks, while any class just has to stand near a berzerker while they rack up kills to bank XP in that perk. It's a fun system that encourages experimentation and doesn't stifle any type of specialisation. The stat boosts don't make any functional difference until you start to ramp up the difficulty, so levelling perks ad-hoc in the lower tiers before jumping into tougher runs is more than viable.

Weapon selection is generous and practically encourages cartoon levels of violence, with incendiary trench guns alongside zwiehander swords and laser guided buzzsaw launchers. Guns are balanced and feel individual; a lot of care has gone into the weapon set and it shows in every meaty shotgun kickback and precise grenade arc. Wielding the arsenal is a collection of stock avatars that can be fully customised with cosmetic gear rewarded in-game or purchased from the online store. The survivors are comedic archetypes like a psycho ex-teacher and historical re-enactment enthusiast, with a decent selection of dialogue and tongue-in-cheek clothing sets.

The main survival modes available on release – one against AI and one versus player controlled zeds – offer a middling selection of maps, but what is there is worthwhile until extra content starts to roll in. These levels are well thought out mazes of death with the right balance of open areas and choke points; with doors that can be welded shut to buy time and unpredictable enemy spawns, the levels don't wear out their welcome too quickly. The environments look great, especially when the viscera starts to hit the fan and the enemy waves start to pour in; apocalyptic Parisian streets, a labyrinthine prison, and a nightmarish Hellscape are highlights. It's also notable that performance doesn't tank when action gets extremely busy, keeping a smooth framerate with large numbers of enemies and environmental effects on screen.

The 'zeds' (the games affectionate term for its antagonists) themselves are great to look at and fun to dispatch. Weak annoyances like the Cyst and Clot make up the meat of the horde, with medium threats like the Siren, Bloat, and Gorefeast employing projectiles and melee weapons to mix things up. Crawlers can be terrifying if they catch you without the rest of your co-op buddies, dropping from the ceiling and scuttling towards you en masse and at speed, while Stalkers employ Predator-like camo to sneak up and roundhouse kick you in the face.

Then there's the big fellas: Husk, Skrake and Fleshpound – variants of a bullet-sponge brute class that are guaranteed to mess up the dynamic of any group on higher difficulties. Finally the boss waves offer a mixture of offensive attacks, in addition to further assaults from lower level zeds. With multi-stage health bars and aggressive AI, the two big bads on offer are the real challenge of Killing Floor 2. The Patriarch employs devastating projectile offence with a one hit kill melee for anyone unfortunate enough to get in close, while Dr. Hans Volte – complete with teutonic accent and mad scientist getup – spews noxious gas that can splinter a close knit group, before letting loose punishing electrical attacks. Fighting these guys rewards cooperation and map knowledge, and taking one down can be hugely cathartic.

Conclusion

Killing Floor 2 is a great co-op experience with pick up and play appeal that promises to keep delivering with frequent updates and community driven content. It's been a long time since there's been such an addictive standalone co-op game on the PS4.