Killing floor two is nothing but a zed game. This zombie game is sweet with many different weapon choices you can buy at the end of each wave. You can have 4 waves all the way up to endless waves in which endless just like cod only lasts until you die so if you are good, you can keep going and going nonstop.
It is multiplayer, co-op or solo so you can play with friends, others or by yourself. It is not crossplay so console cannot play with pc.
Each map has a collectible that you have to find and it is up to 10 collectible on each map and sometimes it is the same and sometimes it is different so good luck on trying to find it. Each holiday there are maps for it like in Christmas the zeds are dressed up as gingerbread man, elves and more.
When you complete each wave there are boss modes that you have to get through and it is really hard since a lot of the bosses includes waves and waves of zeds.
If you are happening to play on steam, you can basically sell your loot, weapons, and things you get from the game in the steam market and earn a little bit off of it which is nice but sometimes it will take a little while to sale.