Half Life 2 Silver via Steam should be a required purchase by everyone that has a PC capable of playing the gamein 640x480 low detail at a solid 25-30fps.

The game is total sex and it comes with enough extra shit and there's enough free shit available that you quite literally do not need any other PC games for quite some time. Not days. Not weeks. Months.

I still have a couple of big Half Life SP mods I need to play (Heart of Evil and Hour Glass) :(