You must have heard about Killing Floor, if not about the one of the games then you have heard complains about gore level in the last installation in this franchise. This franchise went through a lot to come where it is now. You have to realize that first Killing Floor was just a mode, and later it was made into a real standalone game. For better understanding of this franchise I will convey thoughts of Tripwire team ( developer ) on this franchise.
Killing Floor, the game not the mod, was released at the time when Left 4 Dead 2 was a most popular online zombie game and the success of the Killing Floor was doubted because of that. But this game had some differences from Left 4 Dead 2 and those differences were things that made Killing Floor a successful steam game. First difference is that KF ( Killing Floor ) had no objectives, only goal in this game was to survive waves of zombies. The concept where in one point you are struggling against a 100 zombie or more wave, and few minutes after that you are being given minute or two of rest, to equip yourself for the next wave, was a paradise to many players.
The option to create mods for this game made this game really player friendly. Tripwire created this game to be modded by players, and that was proved to be a great success. Some of those modes added new monsters, but the most important things about mods is that they brought a number of new maps to major community. Every map that was properly balanced was given a go from Tripwire team and was accepted into the map rooster of the game. This practice continued and it’s used in new Killing Floor game too. New addition to modding capabilities of the new Killing Floor game is that people will be able to create new classes and new weapons that will, if proven good, be included in TF 2 game.
New addition in KF 2, that pleased many players is destructible environment.
The most important thing includes lights and destructible walls and doors ( in old KF you could defend on one place all the time and doors ,if busted in one wave, could be welded in next one, while in new one longer you stay in one place lights will get destroyed and your vision would get limited. Door once welded and after that destroyed by zombies, can’t be repaired and in addition to that zombies will destroy walls to get to you and eat your brains ).
Tripwire has a very healthy relationship with gamers, they give stuff for free, and they allow modders to mod their game from the beginning, and that is why this is the right mindset of a game developer.