Here's a game that's unforgiving in difficulty, Syphon filter for the original Playstation. Even on the normal setting it is inhumanly difficult for most players.
Also, I like to point out Far Cry on Normal. I have had a lot of trouble with that game, and near the end, it just becomes extremely hard for me to play well.
But yes, Half-Life is a hard game, but hey the older games where harder than the ones today. What where you going to expect, AI that's as good as COD4's? Yeah, I think you learned your lesson.
Oh Ninja Gaiden? Geez, that's a VERY hard game.
Wait... MIKE TYSON'S PUNCH OUT for the NES. After 55 failed trys, I stop playing, and go to my room crying. Yeah, never did beat Tyson. He'd look at you funny then he'd kill you instantly. So, that's practicly impossible, but only a couple of people I know can do it, but that's only because they have no lives.