Anachronox. It's occasionally funny, sure, but that can't hold a game together. The combat was just horrible.
Evolva. The premise is interesting and should make for a fun game. Unfortunately, the gameplay just doesn't hold up. It's a little awkward. Plus, something about the graphics is just... off.
Lionheart: Legacy of the Crusader. The setting is pretty cool, but I found it to be too hard to be fun. It's one of those RPGs that seems to have had a specific build in mind, and I was unlucky enough to choose the wrong build.
Desperados. Being such a fan of the Commandos games, and hearing this one was similar, I really wanted to like it. However, it was way too hard for my tastes. The game requires perfection, and unfortunately, I just can't play it perfectly.
Divine Divinity. To this day, this is the game I am most disappointed with. A lot of the games I buy here on GOG I buy because they are on sale and look a little interesting. I figure if I don't like it, I didn't pay too much for it so it won't be much of a loss. However, I had been looking for Divine Divinity for over a year. I read about it somewhere and I thought it looked awesome, but I couldn't find it. And then one day I hear about this site called GOG, and they have Divine Divinity on sale. I joined GOG and bought it... only to be utterly disappointed with it. It just isn't fun. At all. And the story isn't great either (yes, I realize that's opinion, but whatever).