> cryBlue Lacuna, by Aaron A. Reed, is the deepest and broadest piece of interactive fiction I've played. Granted, it's not a community I keep up on (regrettably), but I enjoy it more than Jigsaw and Galatea which were my two favorites. There is a prequel, Blueful, which is a bit too pretentious for me.
You feel only the mounting dread of impending loss. The loss itself is not yet real.
Spelunky (which really needs a better homepage at this point) is a roguelike platformer. By this I don't just mean the levels are randomly generated (although they are) but that it's difficult but rewarding, its interactions are multifaceted, it's short, and it's score-focused. It is also best played on a gamepad. It's by Derek Yu, who is one of the co-authors of Aquaria.