#1 Any Cinemaware title (Wings, Lords of the rising sun, Defender of the Crown etc), Amiga(truly great in its time)

#2 All of the Gta series except 2. Pc and Ps2, Ps3(just genius)

#3 Another world. Amiga.( An epic masterpiece)

#4Tenchu 1. ps1 (for being the first true ninja game)

#5 Any Total War title (Shogun, Rome, Midieval and Empire) PC (redefining the strategy genre on a grand scale).

Honourable Mention,

Wing Commander 3.ps1&3do (great story,great gameplay and Ginger Lynn)

Its so hard to choose. But these five should do.