"How did you think you finished portal 2!?"
I left the game just after Wheatly betrayed me and I thought it would shortly be followed by a boss battle with him. Didn't realise there would be a load more levels, let alone adding more puzzle mechanics.
Spoiler for Hidden:
the end isn't even the end. you haven't finished the game if you haven't played the extra coop levels.I plan on playing the co ops. I like a good co op game.