Cave Story 3D, a "fully reconstructed in 3D" version of Studio Pixel's shooter, on the Nintendo 3DS -- Nicalis will be handling development duties. This means that there will be polygons and, utilizing the tech of the 3DS, certain environments will have a kind of curvature introduced. "This curvature can be accomplished by defining a 3D spline that directly and uniquely maps to the 2D grid that the game is actually aware of," says a preliminary fact sheet for the game. So, in layman's terms, it's still 2D, but projectiles and characters will move around these curvature points as if it were a 3D space.
Everything else about the game is still pretty much the same: you explore; you shoot guys; you get experience and upgrade stuff. We weren't given a launch date for this latest port (Cave Story is currently available on the PC, WiiWare and DSiWare), but we've got a gallery of concept art you're free to peruse.
Update: NIS America announced a summer 2011 release date for this 3DS remake.