Which PC game is the best?

I tend to play shooters mostly, although I do get caught up in the occasional RPG. Right now I'm stuck on the S.T.A.L.K.E.R. games, and I'm still playing Team Fortress Classic after many years. Occasionally I'll play a few games of Solitaire as well.

I'm not the biggest game player when it comes to laptops and PCs. I used to play on my playstation and indeed my gameboy constantly as a child, but as I grew older I lost interest in this area of life. However there is one PC game that I have loved for many a year, and that is the Sims. I started out playing the original Sims, and went on to owning all of the expansion packs. I was so engrossed with this that I did not bother with buying the Sims 2 until a few years after its release when it went down in price, and finally purchased that along with a few of the expansion packs. Now that is providing me so much fun that I am not even stepping towards Sims 3. Though perhaps when that too lowers in price I may give that a look at too!