I unlocked that gate, it's still more backtracking then I'd like. Also, in seeing how people are beating enemies I'm finding that the game really doesn't reward stealth, which sucks, because the way enemies are laid out you would think that you should stealth as much as possible until things go sideways, then mop up the enemies that are left. But that's just not how the game seems to work.
I haven't played it since re-installing it, but I will stress yet again that I feel that I have picked up the finer points of the game very quickly, but the game itself constantly moves the goal post on how to play it effectively.