Great article on DX8/DX9 comparison over at Anand

[F_A_L_C_O_N]

here is the article

difference on the 2nd page (linked) between DX8 and 9, when looking at the water, is incredible

[fire]

Thats some crazy stuff. I wonder if all the benches fron NV that people see on the game are from DX8 or 9?

[Martin_89]

wow that second picture with the water, the difference is amazing.

[F_A_L_C_O_N]

Backward support is quite incredible as well:

"While it may not look as good as the DX8 and DX9 codepaths, the DirectX 7 support in Half Life 2 is nothing short of incredible. Older card owners should upgrade their CPUs as needed but needn't upgrade their graphics cards unless they want better image quality, in terms of speed, even something as slow as a GeForce4 MX will do just fine."

and if you own one of the older cards, this is well worth reading, before you upgrade:

"If you've got a NV3x part your Half Life 2 performance isn't too bad so long as you stay far away from the DX9 codepath; as a DX8 solution, the NV3x GPUs do just fine, there's actually no reason to upgrade unless you want better image quality, since the frame rates they will provide are pretty high to begin with. The same can actually be said about the GeForce4; we found the GeForce4 to run Half Life 2 extremely well in DX8 mode, and the image quality is quite good. Be warned, if you are upgrading from a GeForce4, you are going to want to go for something no slower than the Radeon 9700, otherwise you will get an increase in image quality but a decrease in frame rate."

They have really done some job with this HL2 engine, no wonder it took them 2 years longer then expected