Wow, HL2 is so well-programmed that it can run on some pretty old, oudated machines, yet this is an aspect that receives criticism. What do you want them to do? Make it dual-core only so you and 3% of gamers can play it?
Although I pick HL2 for having superior multiplayer (HUGE, +excellent mod support makes a game that lasts, much more important than other parts), story, sound, performance, etc etc, Far Cry did blow me away with it's amazing environments and graphics. I bought a Barton and a 9800Pro and Far Cry was one of the first I tried with my new computer. Very immersive game, but the whole package wasn't quite on par with HL2, although it did get released a bit earlier (still, fvck the a-hole hackers that delayed HL2 in the first place).