Faxanadu (1989 - NES)
Faxanadu is a side-scrolling NES adventure game that has been one of my favorites since I was a teenager. It's sort of like the sidescrolling areas of Zelda II: The Adventure of Link, only without the overworld. It has very detailed graphics, a decent soundtrack, and a reasonable amount of exploration and item-finding in a "Giant Tree"-themed world. The game's unusual settings, which include a haze-covered "World of Mist" and the twisty hollow branches of the World Tree, are unique and memorable. The challenge tends to be on the low side (as is often the case with adventure games), but there are some good puzzles (I think everyone who's played it will forever remember the three fountains quest), mazes, and at least one boss that took me several attempts to beat even with a full stock of life potions.
The plot, which involves dwarves being turned into monsters by a strange meteor that fell from the sky into their domain, is rather basic, but has a few twists that make it interesting. And the ending is really neat - definitely worth playing through to see it.