Portal
Well, I'm bored but don't want to go outside (yay air purifier), so I'm basically glued to the computer.

Portal... If you don't know, it's a short, episode-length game that comes with Valve's Orange Box. It's a first-person perspective game using the Source engine, apparently set somewhere/sometime in the Half-Life multi-verse. Unlike Half-Life, it's not really a shooter at all, per se, but more of a puzzle game.

The basic hook is that you get a portal-creating device. You "fire" once at a flat wall, and it creates a blue oval. You fire with the other mouse button and it creates an orange oval. Once there are both ovals, they form a single portal - you (or anything else) can see and pass through it freely either way. You can fire as much as you like, but there's only ever one portal, so if there's already a portal and you make a new blue oval, the last blue oval disappears and the new one connects to the orange oval - which in turn remains in place until you create a new orange oval.

Oh, and you're mysteriously immune to falling damage. Which, as it happens, is a really good thing, since you can create portals in walls and ceilings, and some of the puzzles involve moving at remarkably high velocities...

With that fairly simple premise, they create a wide variety of environmental challenges, each more interesting than the last, and combine them slowly and steadily over the game. The whole game is in some sense its own training; it's really kind of neat how they slowly introduce game mechanics, show you how they work, make you use them a couple times, and then throw in twists and combinations. I never got completely stuck, but a few spots took a fair bit of thinking to figure out.

The story, what little there is of it, is also quite interesting. It's definitely in the Half-Life 2 minimalist storytelling style, where you can just barely sort of piece things together by the very end. Much of it is cutely disturbing, or disturbingly cute, or something like that. I'd say more but I really don't want to spoil it.

Anyway, I highly recommend it.