Valve Software is best known for Half-Life and Half-Life 2, which are both revered as some of the best first person shooters ever made. In October 2007, Valve released The Orange Box, a long awaited compilation of Half-Life 2: Episode 2, the second episodic expansion to Half-Life 2, Team Fortress 2, a team-based multiplayer shooter, and arguably the oddest of all, Portal, a first person puzzle game.

Developed by a group of former students, Portal is the shortest, sparsest, and least hyped part of The Orange Box, but it is in many respects the best. Portal blends humor and mind-bending puzzles into one of the best games of 2007.

In Portal, you play as an unlucky test subject of an AI gone mad. Forced into experiment after experiment, your only choice is to navigate deadly obstacles with the portal gun, or as it’s formally called, the Aperture Science Handheld Portal Device.

The gun fires two linked portals: what goes into one comes immediately out the other. The concept is difficult to grasp at first but is incredibly freeing, and it leads to some of the most imaginative gameplay in any genre, not just the first person puzzler, a category that Portal practically invented by itself. Jumping in and out of walls and floors, maneuvering energy balls into generators, and dropping boxes onto turrets is an exercise in quick thinking and timing.

While solving puzzles, you are taunted, encouraged, threatened, and lectured by GLaDOS, the only speaking character in the game aside from a few turrets and one of the best written characters in a videogame in a long time.

The rogue computer is reminiscent of a malevolent HAL 9000 or SHODAN crossed with the dry wit of a comedian, and the expertly acted voice that ping pongs from threatening to manic serve as a perfect complement to the puzzles.

If anything, the writing sometimes overshadows the gameplay, especially in earlier levels, where once the basic concept of portals is grasped, the difficulty stays at an unduly low level for too long. Valve purportedly tested Portal over and over again to make sure players never got stuck, but this diligence may have paid off too much, and most gamers will find themselves wishing that Portal was a little harder.

Bonus maps and challenges similar to the achievements available on the XBOX360 add both time and difficulty to the game for those willing to attempt them, but Portal still suffers from being short and easy. With the exception of GLaDOS’s monologues, the graphics and sound are sparse.

Whether this effectively recreates the feeling of a test chamber or simply annoys you depends on your aesthetic sense as much as it does the game. For what it’s worth, the clean white walls and gray and white tiles benefit from The Orange Box’s updated version of the Source engine, which adds motion blur, depth of field, and other fancy things to keep the game looking fresh, if not appealing.

The music fades into the background as you concentrate alternatively on GLaDOS and the puzzles, and it sets the mood well, but the ambient soundtrack pales in comparison to the song that plays over the end credits.

Composed by nerd and humorous songwriter Jonathan Coulton, the song became an instant classic, and whistling the tune in a room of gamers can elicit an impromptu performance. Full of black humor and a few in-jokes, the credits are a perfect example of what makes Portal great.

This small addition to The Orange Box, now available as a standalone game on Steam, tries something different, succeeds wildly, and earns itself a place in gaming history. It is a must-buy, and while even the bonus maps and a second playthrough may only last you a few hours, user created maps are already available. Either way, Portal is a classic that no gamer should pass up.