Name: Half-Life: Uplink
Developer: Valve Software
Publisher: None - demo, released over the Internet
A short game created to demo the engine, setting, weapons, and enemies* of Valve Software's masterpiece, Half-Life.
Unlike the usual demo format for other games, which was "grab a few levels out the full version, make sure it ends on a huge anti climax, and make none of the story make sense, and generally piss the player off", Valve put thought and care into this demo, and it shows. The demo isn't just a few levels out of the game, it's a completely new adventure, set in a part of the Black Mesa complex which isn't visited in the main game. The basic plot of the demo (which takes an hour or so to play through) is that to open the reactor blast doors and escape from a section of the complex, the all clear signal must be broadcast. Unfortunately, the only way to do this is directly from the uplink tower, and it's full of radiation. However, Gordon Freeman in his HEV suit is naturally nominated by a "friendly" security guard to go in there, send the signal, and get back out. Alive. Easy.
The demo features fights with aliens, marines, a bit of jumpiness, some radioactiveness, and some scariness, a hugely atmospheric ending, and some shooty death. Everything that the real Half-Life offers in a nice short package. It has an absolutely incredible sequence of scripted events from the moment you get to the uplink tower (those who've played it will know what I'm talking about) and it's every bit as fun, while it lasts, as the complete game. Half-Life: Uplink is included with Half-Life game of the year edition, and is quite honestly, the best demo I've ever played, of the best game I've ever played.
Half-Life: Uplink is available to download at www.fileplanet.com for free, or on PC magazine cover discs, or as part of the Half-Life Generation compilation pack.
* - Thanks for correcting me on this, amib.