Team Fortress 2 is an entirely multiplayer game by Valve, and is featured on "The Orange Box".
Team Fortress 2 has selected character load outs. Examples of this being classes such as the spy, the heavy, the engineer and scout, with many more. Each character has been designed by Valve to make each a different experience. Characters such as the heavy will be slow, have a large amount of health, and a large mini-gun, whereas a character such as the scout can move quickly, has a shotgun and bat, but very little health. With the different play styles, it should be easy to find a preference, so you don't feel left out like a little boy on a swing set watching his friends play football (Soccer).
The maps for Team Fortress 2 are similar, which can be a good or bad depending if you're a pessimist or optimist. On one hand it allows you to learn the map, find good vantage points etc. However. With there only being 3-4 maps, there is little in the way of variety.
Team Fortress 2 is a great time killer. So in conclusion, you should play TF2, Orange Box or not, besides, you could always play worse games than Team Fortress 2... Like Call of Duty.