Retro Game Challenge comes out in North America next week, but Japan is already one game ahead of us -- the sequel, Game Center CX: Arino no Chousenjou 2, comes out there on the 26th. Famitsu has screenshots of two brand-new games in the sequel, and four ... kind of new games.
Guadia Quest Saga is a sequel to the original game's Dragon Quest-like RPG, released late-ish in the (fake) Famicom's lifetime, in 1991. GunDuel, the sequel to StarPrince, is a vertical shmup with much more detailed backgrounds.
Four "rare" games are only available in the (in-game) game shop, presumably because your character can't afford to buy them! Cosmic Gate: MASA-X version is a port of the first game's Galaxian-like shooter, made in the style of MSX computer games. Rally King EX is a special "time trial" version of the original's racer, and StarPrince SA is a special version of StarPrince in which players have just a few minutes to accrue a high score. Perhaps weirdest of all is Karakuri Ninja Haguruman: Koume Version, which was (in the alternate universe of the game) a special release of Haguruman with the hero sprite swapped out for his sister Koume, given to members of that character's fan club!