People will indeed argue GTA fanbase has increases dramatically since the days of 2d GTA and argue DS userbase vs PSP's.
However you make an excellent point about 2d vs 3d. Most GTA fans grew up playing GTA:SA not GTA or GTA II. The DS version seems a tremendous step backwards for them and while that's fine for those that played the 2d originals it'll be a hard buy for those that didn't.
For example people not only accepted but creamed themselves over Megaman 9. But if you made a 2d Halo no one would want it except an intriped few.







