Cortana... Halo 3
Don't get us wrong. We love Cortana. In a trigger and testosterone-happy war game that often plays like a military recruitment device, she is the one glimmer of personality and spunk. In the company of a largely mute protagonist, she is the one voice of conscience, reason and comfort. She may be nothing more than a piece of computer software, but we'd still do anything and go anywhere for that bundle of 1's and 0's.
Which, ironically, is why we find her so friggin' annoying in Halo 3. Look, Cortana, we already agreed to rescue you, remember? The whole promise thing at the end of Halo 2? Yeah... So please stop interrupting us every other step to harp about "sacrifice" and "hardship." Please stop locking our controller and interfering with our screens every other level so you can babble on and on about defying "gods and demons" and loosing "damnation on the stars." You sound like you're on crazy pills.
Of course, you could have frozen the game to warn us that the level you're imprisoned on is the most painful and frustrating since Halo's Library. Oh wait, never mind - that actually would have been helpful.