LABYRINTH / LucasArts / Apple II
This was one of the first games from LucasArts (when they were still called "Lucasfilm Games") and I believe their first real adventure game as well. If you haven't done any prior research on the game before playing (ahem) it initially appears to be a text adventure, but with a "command wheel" type of interface instead of a parser. Hang in there long enough to blunder into the movie theater, buy some popcorn and find the Labyrinth theater, however, and the game turns into a graphical adventure proper.
Of course, it's based on the oddball 1986 fantasy movie of the same name. I feel compelled to warn the Underage Jennifer Connelly Brigade that while you get David Bowie in all his pixellated glory, the main character is actually chosen and named by you (you can even pick a male character if you like.) There's no baby cryin' hard as a baby could cry either, you're just trying to bail your own ass out of the Labyrinth. You get a 13 hour time limit at the outset, which apparently actually is counted in real time; it can be extended even further by reading a book you find a little ways into the game.
The engine used in Labyrinth is a primitive, experimental version of what would eventually become SCUMM (as of Maniac Mansion.) The game is kind of structured like Dragon's Lair meets an adventure game; instead of exploring and backtracking through a cohesive world a la King's Quest, you hop from one self-contained scene to another (usually based on the movie.) You'll need to bring a few items from one scene to another, but mostly they are solved on their own. Traditional adventure game puzzles are actually kind of thin; many scenes are just arbitrary mazes where you have to trial-and-error the right path through, and some have arcadey elements like crossing a slippery bridge or having to lure goblin guards over trapdoors.
While the game is conceptually pretty cool and the whole thing is really pretty impressive for a 1986 release on the less powerful computers of the time (it only came out on the Apple 2 and the Commodore 64), it's a little tough to come back to and play after all this time. You'll need to have seen the movie to understand the otherwise totally random solutions to a couple of puzzles. And everything is always a little bit slow and clunky - movement, screen transitions, selecting commands off of the command wheel. The time limit isn't an issue at all, as the game only takes about 30 minutes to complete if you know what you're doing, but everything from the faux-text adventure onward is always at least a bit irritating in some way or another.
Big fans of the movie will likely find it worth putting up with, however, as it's pretty much the only attempt at actually rendering the film world in its totality in game form.