Mind=Blown.

[Teh_Hobo]

Some (most?) of y'all may have seen this, but it has just blown my mind.
Half Life 1 Completed in half an hour.
This is just ridiculous.

[Corgatha Taldorthar]

One wonders how much he had to practice (read: replay) the game in order to be able to beat it so quickly.

[Tapewolf]

People have done the main quest of Morrowind in about 7.5 minutes.  This is very tightly-optimised and presumably requires a lot of practice, but people have done it.  Among other things they murder one of the Mages to get the levitation staff and use all three of the mad falling Mage's jump spells.  Naturally, they do not use the magic gauntlets to protect themselves from Sunder and Keening.

[TheDXM]

One wonders how much he had to practice (read: replay) the game in order to be able to beat it so quickly.

A lot I'm sure. Part of the appeal is the technical examination you have to go through to try and find the fastest way to get through an area. On top of things it seems he abused a few glitches and knew exactly how much health to maintain point for point during the whole ordeal which shows how thoroughly you have to understand the game to be able to pull something like that off.