By far the best game ever made, at least in its time; Half-Life 2 is and was the most realistic game ever; HL2 crazy!!!!
This game takes place just after the first, the story is compelling, the gameplay is crazy and the physics are almost more real the reality itself. The game itself is a masterpiece, the digital actors/actresses, the designs, and the gameplay and its events will drive you to want to play even more.
The commands and movements themselves are pretty standard, but the added feature of drivable vehicles makes gameplay more intense. The time it takes to play is great, but the rewards and enjoyment makes it worth the while.
***Just a short mention on online play
The online play itself is great and the teamplay can drive you to becoming fully devoted. Also the mods and their servers are worth their weight in gold aswell.
Buy this game if you don't have it, will you still can; it took me a long time to find mine and I just got it not too long ago.
Good luck and happy fragging.