Perhaps a little slow off the mark, but Anandtech's Half-Life 2 CPU Performance Analysis is here, and the best bit has to the Intel vs. AMD analysis. Basically, AMD chew Intel up and spit them out:
While you can argue that AMD's performance advantages in the other tests aren't noticeable on a price-for-price basis, you can't argue with the results here. At the $280 - $290 price point, AMD's Athlon 64 3500+ delivers about 15% more performance than Intel's Pentium 4 550.

The margin is even greater at the low end, AMD's Athlon 64 3000+ is 23% faster than Intel's similarly priced Pentium 4 520.

At the high end the advantage is equally in AMD's favor, with the Athlon 64 4000+ holding a 22% advantage over Intel's fastest Pentium 4.

Conclusion? Don't look any further than AMD for the best gaming CPU, and Half Life 2 further cements AMD's reputation as the gamer's CPU.
[The article]