If you are wondering whether Half-life 2 is as good as everyone says it is, then stop. It is, and much more.
I love both the single-player portion of Half-life 2 and the multi-player portion, Counter-Strike: Source. The single-player campaign is pretty long, but you can finish it pretty quickly if you really get into the game. It is also very easy to play, even if you are new to the FPS world. It has a great Sci-fi storyline, and the graphics are just plain AWESOME. That said, you will need a pretty good computer to play this game.
The physics in the game are also very believable, and every item can be used against the enemy, whether it is a wheel barrel or rubber tire.
Counter-Strike is also fun, not to mention addictive. Voice chat works very well, and the physics return in the online mode.
You MUST have an internet connect to install the game. Keep that in mind.
Half-life 2 is one, if not the best, first-person shooter ever made. A perfect 10.