Criminally underlooked at the time of writing. Surprisingly atmospheric, backed with excellent and somewhat unnerving sound design, and a great John Carpenter-inspired soundtrack. Fog effects are well-handled, and the lighting can be impressive. All backed with an excellent 80s-grindhouse horror aesthetic that brings out colors and shadows almost like a Giallo horror film.
The game is enjoyably schlocky, with gore and dismemberment up the wazoo, and intensely satisfying gunplay, with snipers stealing the show with the well-done mechanics of the Sniper Elite games, but just as much satisfaction coming from the other firearms, and a variety of explosives and traps you can lay. But even with this, the game is challenging, with a large variety of enemies (ranging from your typical nazi zombie, Ray Harryhausen-esque skeletons, the ghost of nazi generals, fire-spewing demon incarnates, crazed-slasher chainsaw maniacs, and much more) that can be a challenge to take out and can manage to either overrun you or sneak up on you from behind. Zombies resurrect with satanic circles bringing them back to life until their brains are blown out or you dismember them beyond repair. The locations are vast and varied, both in layout and theme, ranging from streets of Berlin, underground war bunkers, demonic infested forests, high-speed trains, haunting church chapel catacombs, and much more.
It's co-op is a lot of fun, allowing strategy and different play-styles to mesh well, to find the perfect sniping spot to pick off zombies and compete against friends for the highest scoring or longest shot, to go lone-wolf and carry the most kills for your team, or to come together when plans go awry and struggle to survive by the skin of your teeth. But even with the co-op focus, the game is also an excellent experience single-player, the game allowing you to scale how many enemies there are (enemies for one player to four players, or if you're insane, 'Elite' number, which spawns those who third for stupidly large hordes and a challenge), among three different difficulty levels.
A lengthy meaty campaign with 15 stages (each being around an hour long), side-missions to do in the third episode, an addicting Horde Mode, all at a reasonable price tag. If you love co-op games or zombies, it'll be quite the undertaking to something find better than this. Dumb fun, but intelligent and challenging in surprising ways, it wears its inspirations on its sleeves, but through slick execution and presentation, matched with pulling it off in a way no one has quite done it before, manages to be one hell of a game.