Ok, due to the size and amount of achievements i wasn't able to c&p it, so here's a webpage listing of them. I also located a couple youtube videos too:

http://www.achieve360points.com/game/theorangebox/
http://www.xbox360achievements.org/game/half-life-2-the-orange-box/achievements/

Here's the guy's youtube page in case the videos don't work for whatever reason:
http://www.youtube.com/user/guyandsam

Online/multiplayer achivements: 17
Single-player: 82
Secret achivements: 11
(Note: some secret achivements are single-player ones.)

Whew.

Asker's Rating:

Permalink | Report