Nintendo is retrofitting classic titles for the 3DS, like the already available freebie 3D Classics Excitebike. But as the company reveals in the latest Iwata Asks, they've run into their share of difficulties converting the old titles.
"In the original [Xevious], the game unfolds on a flat surface," said Takao Nakano from special-planning and development. "The moment we made Solvalou float in midair, all sorts of discrepancies arose. For example, when an enemy on the ground fired at Solvalou in the original version, everything was on the same plane, so it didn't seem unusual if the bomb appeared at the same altitude as Solvalou the moment it was fired and then hit Solvalou right away. But with the Nintendo 3DS system, Solvalou is floating in midair. If the bomb suddenly appears at the same time as Solvalou... we were like 'huh? Something doesn't feel right!' Everything was off!"
In the end, Nintendo had to redo the graphics and programming to make it function properly. Other games, like Tennis for the NES, just seemed underwhelming in 3D thanks to its original effect. Excitebike also used a visual trick in its original incarnation, but Iwata says in 3D "the world really expands."