OMG this add-on is just jaw dropping...
check out the insane system requirements:
1 gig of ram
nvidia 6800 or x800 if u want smooth game play, anything less gets choppy on higher resolutions
My friend has a amd athlon 64 3200+, 1 GB ram, and Nvidia 6800GT. He gets around 40 fps at 1280 by 1024 with high details, so that should give you an idea as to how power hungry the game is
I played the game at a friend's house, and it looked absolutely stunning... I love source engine, it's so realistic. If fact, real life graphics suck, so life shud run on source engine