This is what the fps genre is supposed to be. Forget Halo, forget cod, this is the perfect game to get with your new 360
Half Life 2
Half Life 2 Episode 1
Half Life 2 Episode 2
Half Life 2 is worth the price alone. This is without a doubt what a fps game supposed to be. It is challenging, and you have to come up with a strategy on many occasions to get you out of a situation, unlike other games where you just shoot stuff (halo *ahem*)
Enemy design is nearly flawless. There are some combine troopers who are a little annoying, but you've also got zombies, giant bugs, ships, small bugs, quicksand, and who can forget the helicopter. It is very challenging, but not too difficult. You have to think your way through many parts in the game.
The graphics look awesome even though the game is 5 years old, you CAN tell at a few spots there are bad graphics, but this needs to be overlooked considering the age of the game.
Portal
Portal is a unique game that will have you perplexed, puzzled, confused, then when you finally figure it out, you feel like you've accomplished something. It's a neat addon to this package that isn't just a quick fix......it's a complex game that requires a lot of attention and thought.
Team Fortress 2
This is the online aspect of The Orange Box. Its really fun if there a lot of people online, Unfortunately it's rare now since the game is so old. Every now and then you'll get lucky and get into a real good match.
The Orange Box is the perfect game to get with your system. It's cheap, and it will give you many, many, many hours of playing time. This isn't a 20 hour single player game and you're done - there is a lot of things to do in this game and it will keep you busy for a while.