Greatest is too narrow for my liking but +1 to Dragonlord although deus ex's sequel was probably not that worthy of praise.
Also Earthworm Jim, Phantasy Star, Streets of Rage and the "Shining" series are absent (3 guesses who was going through old megadrive games earlier this evening).
If pushed though Mario games are responsible for numerous clones, spin off titles and a whole host of other stuff of which most of it is high quality and drawn in many people that may not have otherwise played games (mario kart and warioware have drawn many people towards my DS and if I were to cite other examples from my experience alone we would be here all night) so nod is due there.