Even the likes of Crysis on the PC, while undoubtedly having better texturing, foliage rendering and a far superior shadow resolution is trumped by KZ2 regarding overall visual treatment, animations, level design, AI and physics. Killzone 2 has gone for the 'BIG' picture and delivers, making other games feel quite flat in comparison.
But its nothing on classics like Half Life, Return to Castle Wolfenstein and Halo:CE. I feel that modern FPS single player have gone a bit stale. Having said that, the multiplayer is better than ever in both KZ2 and COD4.