I recently bought The Orange Box off of Steam, for the PC. Along with these 5 games, I got access to the Source Development Kit, and tools to help me host my own game server, as well as access to constant game updates, ALL for under 30 bucks. This was a very impressive deal. Now, since there are five games in one, I'll give a short review for each.
Half Life 2: This game is pure gold from beginning to end. Playing as Gordon Freeman, you travel to many different highly detailed places on an Earth that has been overrun by multiple otherworldly races. Violent, yes, considering you can sever already gruesome looking zombies in half by firing a saw blade out of a Gravity Gun, but the game is still great. For anyone old enough to play, I'd highly recommend it.
Half Life 2, Episode 1: As an expansion, it adds just a bit more story to Half Life 2, as you navigate Gordon through other puzzles and adventures.
Half Life 2, Episode 2: Another great expansion onto the Half Life series of games, and provides a great cliff hanger for the highly anticipated Episode 3.
Portal: I absolutely love this game. There really isn't any violence (other than you being shot at, but by turrets). This is more of a puzzle game than anything, but it's short and has a little bit of clean dark humor mixed into it. The concept of the Portal gun is so unique, and really fun to play with. I would really recommend this game for any age, as long as they could figure out how to use the device and how the portals work.
Team Fortress 2: First thought that I would like to get out there; it's violent. With that said, Team Fortress 2 is a pretty good game. Now that I think about it, it's the second main highlight of The Orange Box for me. It's cartoon-stylized art direction is high in contrast from Valve's usual realism-based games. You get many classes to choose from, and all are fun to play as. This is a multiplayer game compatible with custom tags, avatars, and headsets, so be prepared for user-made content that isn't age appropriate. I've seen some people make and spray tags that contains some highly suggestively-sexual content, so be prepared. I really wouldn't recommend this game for kids, due to the user content and violence, but it's still a great game for those who are okay with the aforementioned issues.
Source SDK: This is the development kit that you are given when you buy The Orange Box off of Steam, or validate it on Steam. This toolkit gives you the tools necessary for those who are creative and dedicated enough to build their own maps/levels for each game. I've used to create a really cool looking Lego map, complete with giant soda cans and candy bars on the field. Be prepared though, as the Source SDK is for somewhat advanced users, though there is documentation and plenty of tutorials online.
Final thoughts: The Orange Box is an awesome deal. Calling it a "great" deal really isn't enough for what you get out of it, and you sure get a lot more than you expect. I would highly recommend this package for players who are old enough to play it.