Zelda
GTA
Although I still like old-school Marios

Let me think something different this time...

Megaman... Oh, wait... Castlevania... Oh, wait... Final Fight!... Oh, wait... Street Fighter... Oh, wait... Samurai Shodown... Oh, wait... Metal Slug! Oh, wait... Sonic...

Well... Nevermind =/

Mario, it revolutionized 3D gaming as we know it.

Grand Theft Auto. Honestly, it wasn't a very good game in 2D, and now it's one of the most respected franchises ever created. The difference between GTA and Mario, Zelda an all that were those franchises were still good in 2D, but GTA definitely had the best leap.

Duke nukem. By far

Oh wow! I didn't think of that. what Duke game was 2D?

GTA, but then again, I basically missed out on the 2D era

zelda, mario, Metroid

Too few people don't know about the first 2 GTA or else everyone would say it's GTA.

All the spirit of the game was there and it only missed the 3D. Then came 3D, then came success. No other franchise can say it made a better jump from 2D to 3D.

yeah, duke 1 and 2 was 2d. Then came DUKE NUKEM 3D (thats why they called it 3d btw :P)

I'd say...

Duke nukem

Metal Gear

Grand Theft Auto

Final Fantasy

Those are probably some of the best in my opinion. (that i can think of right now