Amen brother. I have over 600 hours on Team Fortress 2 so far, and it has never disappointed me. Valve and Steam do a wonderful job of keeping it up to date and releasing wonderful items/weapons/hats for all. Being free to play brings in more users who were on the fence in regards to the game.
I can not speak for Killzone 3, since I have yet to play it (my internet seems to act up when gaming on my PSN, so I don't play PS3 games online anymore).