Killing Floor 2 is a Survival Horde CO-OP game. Defend waves of Zombie like creatures know as Zeds while running around trying to survive. The game can be very fast paced sometimes as you just clear through waves of enemies all while healing as your getting hit from behind. This game has many different perks that you can use. In this game a "Perk" is technically a "Class", so if your perk is "Gunslinger" your class is "Gunslinger". You can level up your perks unlocking abilities on the way. The higher level your perk the better you do in game. This game definitely challenges players as when you change the difficulty you better be ready to fail.
Pros
Cool Perk System
Fun with friends
Provides a challenge
Cons
The game can get boring after you level a bunch of perks up
Conclusion
This is one of the best Horde games I have played for a bit. It's unique with it's game play and provides a challenge for more hardcore players.