3 in Three: Crazy awesome logic puzzle action from the creators of... well, actually, from no one you've ever heard of.
Marathon: The UnHalo.
The Secret of Monkey Island: A game about pirates and monkeys before that meant what it means now.
Space Quest: The Sarian Encounter: The adventure genre would still be alive if it had more games like this. If it were dead, that is.
Star Wars: Dark Forces: "Stay on Target!"