GTA3 – rekindled my love of gaming, the ability to cause utter carnage was outstanding.
Halo2 – my first online gaming experience.
COD:MW (the first modern warfare) – stunning, stunning game.
Other notable mentions:
Micro-Machines on the SNES – 4 of us playing it sharing a controller between 2.
Elite, obviously.
Harrier Attack on the Speccy – we used to have lunch in a mates house who lived near school and play it non-stop.
Syndicate on the Amiga.