Passage [1] (link via Jason Kottke [2]) is a game that you either “get” and think of as a remarkable experience, or you don't and think it's a pointless game where nothing happens.
I “got” it, and found it deeply moving, for a video game that plays for five minutes (really!) with a 100×16 pixel resolution, simple controls (arrow keys only) and a very computerish sound track. It's recommended you play it once before reading the author's statment about the game [3] (which, oddly enough, contains spoilers for this five-minute low-res simple game).
It also has some glowing reviews [4] (but play it first before reading anything else on this game).
[1] http://hcsoftware.sourceforge.net/passage/index.html
[2] http://www.kottke.org/remainder/08/01/14916.html
[3] http://hcsoftware.sourceforge.net/passage/statement.html
[4] http://www.destructoid.com/-i-passage-i-the-greatest-five-minute-long-game-ever-made-58961.phtml