from what i can tell i'll go with cod4.
i mean come on even though mw2 has so much more cod4 was just a shock to the entire shooter community.
it really combined the best of both worlds in the present/futuristic style of guns and equipment like a tom clancy or rainbow 6 and combined it with the insanly fast paced action of a medal of honor or god forebid halo.
It destroyed anymold it was made from and mw2 is still just as good but the original in this psycho's opinion was better.