I would say impressive graphics play an important role, as if you look at the seperate platforms the best designed games of which graphics plays a as well often sell better. Although I agree that's not the whole story, Tetris for instance is a type of game not requiring good graphics to be addictive and fun. Actually simplicity can be a virtue for some type of games.
> Most PWR Least PWR Winner
> 1. GameGear V.S GameBoy (GameBoy)
IMO Mario and Tetris played an important role, but the Gameboy offered a more acceptable battery-life and was considerably cheaper.
> 2. MasterSystem V.S NES (NES)
IMO Mario won this one! 
> 3. Genesis V.S SNES (SNES)
Again Mario won! Super Mario World was a great game!
> 4. N64 V.S PlayStation (PS)
The N64 took a headstart with Mario64, but apart from Mario64 there weren't many games I actually liked that much... Personally I liked the N64's cartridges better at the time despite the storage short-comings, if only later games came close or go beyond the excellence of Mario64...
> 5.GCN,DC,X-box V.S PS2 ( PS2)
I think it can be debated which platform was weaker, as each platform had their strengths and weaknesses.I think mainly the games which sold well for the PS moved to the PS2 and the PS2 was backwards compatible, so users moved there as well.
> 6. NDS V.S PSP (DS)
Nintendo dominated the handheld console market since the release of the original Gameboy, by targeting a more higher-end consumer which likes PS2-style games in a handheld console and may also be interested in media uses Sony is doing better than any other of Nintendo's prior competitors. I think if they didn't distinguish their product from Nintendo's offerings they probably would have done much worse. I and my girlfriend own a Nintendo DS. Why? We love Mario and the DS's touchscreen functionality for other games, but maybe if in the future if I can access content stored on my PS3 through a PSP, I may buy one of those as well.
