Complexity of Portal 2
(An earlier version of this question asked if anyone has shown Portal 2 to be NP-hard.)

Yes, someone has done this.  Portal 2 is at least NP-hard.

My friend created a proof-of-concept map showing that the ability to beat a Portal 2 level implies the ability to solve 3SAT instances:

http://steamcommunity.com/sharedfiles/filedetails/?id=73499175