Half-Life 2 and Episodes
Half-Life 2 released in 2004 to great critical and commercial success. The Orange Box contains the original game with updated graphics and improvements to the underlying Source engine technology. Half-Life 2 is praised for its solid physics engine with resulting physics-based puzzles, and immersive world and environments. HL2 was also ported over to the original Xbox with many features downgraded, the Xbox 360/PS3 port are nearly identical to the PC version.
Half-Life 2: Episode 1 is the previously available episodic addition to HL2. Once again you take control of Gordon Freeman, fight alongside his partner Alyx and try to take down the Combine the game's main enemy. Episode 1 reuses many of the same gameplay elements as vanilla HL2 with the addition of a few new items and weapons.
Half-Life 2: Episode 2 is a new addition to the series introduced in The Orange Box. The latest installment picks up right after the events of Episode 1, and again introduces a few new tricks to the bag. Originally slated for release as a standalone offering similar to Ep1 in Fall 2006, Episode 2 was delayed for a year and incorporated into The Orange Box release.
Originally started as a class project, Valve was so impressed by the initial demonstration of Portal that they hired the team and made the mod a standalone game. Built upon the Source engine Portal features no guns or weapons of any kind. Instead you have a "gun" that can manipulate portals, which are tiny wormholes that allow you to teleport from place to place. The game is a sequence of rooms each one being its own individual puzzle that requires you to figure out how and where to place the portals to get from the beginning to the end.
Team Fortress 2
Almost a decade in the making Team Fortress 2 was originally set for release in 1998 as the sequel to the popular Half-Life mod: Team Fortress Classic. The original game was set in a modern day military setting, and introduced the concept of class-based multiplayer where each person can choose from a different role with specialized weapons and abilities.
TF2 follows the paradigm of class based gameplay that has since become extremely popular, but goes for an entirely unique design aesthetic. The graphics are cartoony and over the top, with each class being represented by a highly stylized character. The abilities and skills of each class are limited relative to previous offerings as there are only a few weapons and skills available, however Valve added depth through the sheer number of classes and how they interact with one another. For example, pairing a medic with a heavy class grants the heavy character a major boost in health which makes them a far more formidable opponent to deal with.
Differences in Versions
Graphically Valve states that all three versions of the game will look nearly the same, though obviously a top of the line PC will win out. Both the Xbox 360 and PS3 versions of the game do not support mouse and keyboard setups. Valve is directly responsible for developing the PC and Xbox 360 port, while a development team inside of EA handled the PS3 port.