Valve acquired the Turtle Rock Studio while the latter was developing the game, Left 4 Dead. Recently, Valve has released the beta version of the game too.
Valve commented that it can’t assure about releasing other characters right now but will give it a hand in the future.
The new version of the game can be acquired from the workshop of Steam. It was reported that Valve has requested a eminent modder for helping them to work on the game’s development.
For learning the game better, starter kits, maya files and Tutorials are provided. This will help a beginner to expertise the game.