Halo maybe
. halo revolutionized console gaming. console gaming used to be a joke (with some exceptions from the developer rare), but halo totally changed all that. it introduced the two weapon system that really worked well for consoles and the perfect regeneration system. imagine games like call of duty. they are some huge shooters. without halo, they would not have had the features that make them so fun.
honestly, this list is entirely hammered by fanboys. call of duty and half life are great games but they wouldn't be anywhere if halo hadn't jumped the gun in 2001. i know half life and call of duty came first, but hl2 and cod4 took a lot of influence from halo. pretty much ever fps since halo has taken influence from it. it just doesn't get better than this. hands down the great fps experience ever to hit the consoles. the pc version is very good as well.