For the best part of the PlayStation 4 generation, UK-based studio Rebellion has been improving, tweaking, and fine-tuning its co-operative offering through various releases. Zombie Army Trilogy got the ball rolling before Strange Brigade proved three years later that the developer had something special on its hands. However, it feels like all of that hard work has been leading up to its latest project. While it does come with its own set of minor flaws, Zombie Army 4: Dead War is Rebellion's greatest game yet.

If you’ve played any of the team's previous efforts, you'll know exactly what to expect from one of its flagship franchises. This is a third-person shooter which understands and revels in its absurdity. Zombie Hitler may have been put to rest in the pits of hell, but that hasn't stopped his legions of undead once again rising from their graves and casting the world into a state of war. What follows is a tongue-in-cheek, globe-trotting campaign that is nearly just as much fun experienced alone as it is with a group of friends.

That's because so much of what the game asks of you is enhanced by co-operation and friendly banter that playing on your lonesome almost makes you feel like you're missing out on something. It's perfectly playable without teammates, to the point where this is probably one of the most accommodating campaigns on the market, but it can't replicate friendship.

No matter whether you're playing alone or alongside others, however, you'll still be performing the same tasks. From defending key points on the map and baiting zombies into Blood Fountains to putting a bullet through the skull of every last member of the undead, it's a typical co-operative affair. Making your way from one safe room to the next is the name of the game, with a somewhat linear level to navigate and various tasks and side objectives to complete along the way. It makes for an enjoyable 10-hour stretch of missions, but a diverse set of assignments is not what Zombie Army 4: Dead War can boast of.

Where you will find variety, however, is in the game's level design. It is abundantly clear Rebellion made a point during development that every locale the player visits should be vastly different from one another. Capitalising on that to great effect, every environment comes with its own personality, set of quirks, and differentiators to make for a memorable set of missions. Whether it's a romantic boat ride along the French canal, an assault on a volcanic castle, or our personal favourite -- a trip to the zoo -- you can rest assured that each and every new set of levels is going to be wildly different from the last. It makes for an excitingly refreshing experience which keeps you on your toes no matter where in the world you are.

That sort of praise doesn’t extend quite so much to encompass the game’s enemy variety, but there are still more than enough unique members of Hitler's horde to keep you on your toes. As well as the typical walkers, suiciders, and snipers, you’ll need to keep an eye out for necromancers who give those already dead one more shot at survival and Elite enemies -- a real cause for concern. With a gigantic health bar to brag about and destructive weapons to match, they're foes which can quickly turn the tide of battle against you if you aren't prepared. Unfortunately, you’ll have encountered all but everything the game has to throw at you by roughly the halfway mark, leaving the latter set of levels to feel like more of a rehash than anything else gameplay-wise. It never becomes tiresome or boring, but you will feel like you’ve conquered this undead nightmare long before the credits roll. That is except for a truly spectacular finale.

One thing you won't tire of, however, is how good the game simply feels to play. Everything from its responsive controls to smart navigational cues makes for an incredibly smooth playing experience that is complemented further by a 60 frames-per-second option on PS4 Pro. It's a game you could return to a year later and pick the controls back up inside a couple of minutes, making for a title that is exceptional to play in the moment.

That's an aspect more important than you might think as repeat playthroughs benefit your overall rank, lead to weapon upgrades, and unlock more perks. Four characters can be picked between at the beginning of a campaign, each coming with their own bonuses. They're nothing major -- Shola has an increased trap damage radius while Jun moves about the battlefield faster -- meaning that you're pretty much free to choose whoever you like. A persistent level and loadouts are shared between the team so you'll never be left wanting should you decide to try out a new character -- a neat feature which promotes exploration of its welcomingly diverse cast.

Outside of the campaign, a fully-fledged Horde mode is going to have you coming back for more and more. Four maps across various difficulty modes will test your skills to the limit, once again playable alone or with friends. It's most certainly not an afterthought, either. Quite the opposite in fact as new areas open up between waves and ammo refill stations switch their positions, causing you to find a new corner to hold up in the process. With the option of escaping after its 12th wave or fighting until the bitter end, this is a Horde mode primed to impress.

What's more, Weekly Events will rotate in and out with new challenges that reward XP and new cosmetic items. You'll need to take on various campaign levels with handicaps and rules that limit your loadout, adjust the amount of ammo you have access to, and change the effects of certain perks. It's by no means a Destiny 2, but Zombie Army 4: Dead War is a game you and a group of friends could play for weeks on end should you embrace everything it has to offer.

For that to happen, however, Rebellion needs to have gotten things right on the technical side. And it has -- to an impressive degree. We didn't encounter a single bug or glitch during our time with the game while the frame rate stuck to a butter-smooth 60 in performance mode. Those who prefer to up the visuals instead can do so on PS4 Pro, although no matter which option you pick, you're in for one incredibly reliable experience.

Conclusion

Zombie Army 4: Dead War is one of the best co-operative focused games on PS4. Its meaty campaign boasts of impressive level variety, a superb control scheme, and enjoyable gameplay mechanics while a Horde mode tests your abilities to the max. Rebellion has crafted an experience with so much to see and do that it could take a group of players weeks to master everything on offer -- a crowning success for this type of game. Zombie Army 4: Dead War is an absolute riot of a title that is just as cheeky as it is fun to play.