Having issues with the game crashing or with unplayable framerate even with well-above-spec hardware? We've just uploaded a patch to Steam that we think should fix many (but not all) of people's issues. Let us know if this fixes your issue, and if not, which hardware you are using and what problems you are still having!
To guarantee you've got the update right away, just relaunch Steam.
Also check out http://steamcommunity.com/app/361420/discussions/0/152391995406699339/ for info about other issues, including problems with launching the game from some Windows 7 machines.