I would love to see another NiGHTS game, but I fear that the original gameplay may not survive wholly intact. NiGHTS is probably my single favorite game of all time. I say this because I think that its gameplay is perfect, and every other element of the game mixes into that aspect just right. I would be heartbroken if they altered anything about it, and there's a very good chance that they would.
On a different note, I would really like to see Cotton, the queen of cute-em-ups, make a comeback sometime. Since Rainbow Cotton was poorly received due to its lousy control, it seems like the series is probably going to be abandoned. That's a real shame, because the rest of the games aren't bad (OK, Marchen Cotton 100% isn't great either). The first Cotton game was pretty far out for its time, and Cotton 2 and Boomerang on the Saturn are two of the system's better 2D games, not to mention some of the most unique and innovative horizontal shmups ever. Then there's Panorama Cotton, which is like an evolved Space Harrier, and happens to be my favorite game on the Genesis and in the series. Needless to say, it really rocks.