What villain have you faced down has been the most interesting to you?

Kane.

GlaDOS, hands down.

Off the top response is going to be Grahf. But that's because he's the most prominent in my mind. There's probably been a few others I've experienced that I like better, I just don't remember them as well.

Also Magic Emperor Ghaleon. I'm terrible at singling out a superlative example.

Shodan, hands down. In SS1, that is. She grew a bit soft later.

Ah, but I haven't played any of the System Shock games you see, so I haven't faced down Shodan. I do hope I'll do so some day though.

+1

All right then. That's the only excuse I'm willing to accept. It's a computer program. Who cares?

The administrator from the beginning of Fallout 3. Just as I was about to escape from the Vault, I said to myself, "Wait a minute, he's still alive. I read enough comic books that I should know that if I don't kill him now, he's going to come back and get me." So I went back and beat him to death with my nightstick.

Tormented by indecisiveness I'm going to go for a dual answer: Kane from C&C and Dracula from Castlevania.

Sadly, I haven't played any System Shocks either.

I'm going to say Darth Nihilus, from Knights of the Old Republic II: The Sith Lords. I mean seriously, he eats planets. How awesomer can you get?

Darth Sion comes a close second, though.

dawn of war.

Max, dearest of all my friends...:-P
Well, ok. He probably isn't my favourite (if you know whom I speak about), but at the time I liked him a lot.
The most bone chilling villain and the one the most liked by me right now is probably the one from Higurashi (When the Cicadas Cry) series. It's a shame, that even mentioning the gender of this villain could be considering a major spoiler as that is a detective game and you don't find out the identity of the Big Bad until the pre-last chapter (about 80 hours into the game).

Bah! Why didn't I think of him? Ol' Mr. Lem, I think, ties with Nihilus for first place.