With the Value of Valve there's virtually no viable argument against a classic collection.
Half Life 2 + Episode 1 + Episode 2:
These games do a very good job of living up to the task of following what many purists consider to be the greatest PC shooter of all time. Half Life was memorable not only for its shooting but also for the clever puzzle elements and fantastic design. This 40 hour trilogy of shooting sci-fi bliss is easily worth the cost of The Orange Box! Its filled with moments and characters you won't forget.
Team Fortress 2:
Online team-based shooting. Choose from a variety of classes such as Medic, Engineer, Soldier, or a Spy, to name a few, and compete in team based games like capture the flag and Deathmatch. The one thing that made Team Fortress one of my favorite high school hobbies was the Community. That seems to be the only thing missing from Team Fortress 2. I don't know if you can fault Valve for this. The original is a game we played in online gaming's infancy, and while Team Fortress 2 could very well be your thing, it can't possibly live up to the level of enthusiasm players showed 12 years ago.
Portal:
If a friend of yours hasn't already told you about the glory of Portal, you might want to consider the people you hang around with. Portal is by far one of the cleverest games ever created, in virtually every way. Its a bit short, which has left us salivating for Portal 2, but a variety of challenges extend this to at least 20 hours of gaming bliss. Not only my favorite game of 2008, but one of my favorite games of all time.
Counterstrike: (not included?!???!!!)
Counterstrike is not part of The Orange Box. It doesn't not exist for the PS3 or the XBOX360. This makes no sense. Counterstrike is far more entertaining than MW2, and it not being here is a big letdown.
The verdict:
You're getting a very solid game in Half Life 2, with two expansion packs. And they also throw in an online shooter that is worth taking a look at. Even if this didn't contain the shimmering jewel of awesomeness called Portal, it would still be worth your money.