Dude.
I upgraded both my home PCs so that I could play Crysis (and MWLL) on both them and my laptop. That includes power supplies and videocards. But since then I've built a new PC as well, moved most upgraded parts to new machine.
I can play Crysis on my MBP 17", but I think that's probably what fried the video card (I had the older ATI chipset, not the newer 8800 Nvidia crappy chipset). So after getting that fixed, I don't know if I will be using my laptop to play Crysis extensively...without somesort of extra cooling.
So yeah, I did buy it because of MWLL - but I might have bought it anyway because of the game engine. I did buy Warhead just because I enjoyed Crysis so much.