First of all, don't listen to the people moaning about Steam. It's easy to use and as long as you've got better than dial-up internet you've got nothing to worry about.
OK, onto the games. You get the original Half-Life 2, Half-Life 2: Episode 1, Half-Life 2: Episode 2, Portal and Team Fortress 2. 5 games for around £25! Bargain!
Half Life 2 is still, in my opinion, a great looking game and the good thing is you don't need a particularly high spec PC to play it. When I first played this I was blown away by the AI. Throwing bottles at security guards is particularly entertaining. The story is interesting and the main characters are surprisingly engaging; I actually cared what happened to them.
Episode 1 picks up right where Half Life 2 left off, and although quite short, is full of action and will keep you playing.
Episode 2 is relatively short too, but equally as fun. The forest environment is stunning and the action sequences are fantastic.
Portal is a quirky, original puzzle game, which although quite short is very re-playable.
Finally you have Team Fortress 2, a class-based multiplayer game. To be honest, I haven't really got into this. After reading a load of hype about it I thought I'd try it but I have to say it was quite dissapointing for me. Probably more suitable for online multiplayer fans.
Overall, The Orange Box is a must have for any gamer, and at such a cheap price, you can't go wrong.