Nintendo has problems porting some of their classic games over to the 3DS

With the release of the Nintendo 3DS portable gaming console (check out our review here), the company had promised that it will release lots of classic games from its portfolio which will be remastered to take advantage of the 3DS' display, which can display 3D images without the need for special 3D-glasses to be worn by the player. For those who are unfamiliar with Nintendo's “3D Classics” range on its 3DS, it's basically where the game company takes old games (think 8-bit and 16-bit) and gives them a 3D makeover, with Excitebike and Kirby's Dream Land as examples.

Nintendo's Takao Nakano explained that simply converting the old and flat 2D graphics to stereoscopic 3D just wasn't enough and that the games were left feeling like something was missing. In an example he gave with the classic NES shooter game, Xevious:

“With a 2D screen, players had to use their imagination for Solvalou flying above the ground, but on the Nintendo 3DS system, we thought we might be able to recreate it using stereoscopic graphics so it looked like it was really floating [...] In the original version, the game unfolds on a flat surface. 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, 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 – zhing! – at the same altitude as Solvalou… We were like, ‘Huh? Something doesn't feel right!' Everything was off!”

Nintendo has estimated that the workload for a mere port has been increased by at least 20 times, which means that gamers should expect some games (like Tennis) to not make its way to the 3DS or to be delayed.
source: Ubergizmo