I'm going to ignore the nit-picky difference between sentience (anything with a complex brain has sentience) and sapience (humans).
World of Warcraft. Rally the armies of Azeroth in ways no quest line could and annihilate everything that looks at us funny.
Mass Effect. I don't like playing renegade anyway, and sapience would make it that much more difficult to be an unforgiving jerk-ass.
Any game with squad NPCs (Mass Effect, Half-Life 2 leap to mind) will be easier since my squadmates will hopefully stop derping into the gunfire. Also, losing a comrade, even if they can be brought back with a dose of first-aid kit (or whatever equivalent there may be in a given game) in a minute.
Half-Life 2. Tell Alyx Vance how I feel about her. I mean, it's so blindingly obvious that she wants to get into the HEV suit with Gordon - if memory serves, she says something very much like that in one of the episodes - and it'd satisfy the romantic in me, certainly.
Captcha: (C6H5)2CO gembiic. I looked it up, that first bit is the chemical formula for Benzophenone. Oh well, at least it has yet to ask me to enter calculus symbols or something equally asinine.