The Orange Box includes the original Half-Life 2 and Half-Life 2: Episode One. But there is also new content included:

• Half-Life 2: Episode Two -- the second installment in Valve’s episodic trilogy advances the award-winning story, leading the player to new locations outside of City 17.
• Portal -- a pioneering type of single player action game that rewrites the rules for how players approach and manipulate their environment – much like how Half-Life 2’s Gravity Gun reinvented the way gamers interact with objects in the game.
• Team Fortress 2 -- an all-new version of the legendary title that spawned team based multiplayer action games. The game’s daring new art style features the most advanced graphics of any Source-based game released to date.

If you're a Half-Life fan you really should buy this amazing pack and if you didn't play Half-Life before, this is a really good reason to start playing!