GTA San Andreas - had everything. Violence, gang banging turf wars and drug dealing. Mad afro haircuts and complete customisation of clothes, tattoos etc. Wicked sense of humour and great villains.
Legend of Zelda: Ocarina of time - a game full of magic and wonder.
Elite - the first truly open nonlinear game narrative. You could trade, fight, be a pirate, or a bounty hunter, or just roam the universe trying to see everything and failing to dock to the Blue Danube.
Batman Arkhum Asylum - a perfectly executed game. Great Stealth, great trippy sections featuring the scarecrow. The game made you feel like batman, unlike most cartoon games Ive played.
Fallout new vegas - massive, well scripted game with lots of factions. Bethseda still make intelligent RPGs that give weeks of immersive gaming time.
Mass effect 1 - the best characterisation of any game I've played.
Tiger Woods Golf - the version when they had limited tiger vision. Helps if you're smoking really strong weed with a mate, for added giggles.
Bubble Bobble - played this forever as a kid.
Fifa world cup 2010 - played footy games more than anything else. This is a good one.
Football manager on the spectrum. - the first football manager game ever. I once played it non stop for 17 hours.
Neverwinter Nights - not the original game but a set of modules some genius designed and left on the net for everyone to play.