I only play two games on the PC one of them is the Sims 2 which is one of my favorite's there are around 15 expansion packs for the games I've got 13.
It's just very entertaining and you can spend hours on it without realizing.

Now one game I'm totally hooked on at the moment is Battlefield 2, I play online and I love it I think its a fantastic game, the graphics are good and the more you play the quicker your ranking goes up and you can unlock better weapons.

I have also played Black & White 2. It's ok as you can choose to play good or bad but I prefer games where you can play online with others.