I'm a medium/normal player for the most part. Only a truly satisfying game deserves the honor of being played at higher difficulties.
Also, I am a fan of the adaptive difficulty in modern games like L4D. Some might call it a cheat, but it largely works as intended. AI Director strikes me as a pompous euphemism for "adaptive difficulty", though.
But it's Valve. They made Portal. They can do no wrong.
Also, screw you, Capcom, for your "You suck at this game, wanna play on easy?" option in Devil May Cry. Excuse me for sucking, but if I wanted to play on retarded, I would've selected retarded from the menu.
On that note, the "Dante Must Die" difficulty setting is probably the most clever name for such a thing I have seen in a game. Appropriate, too.