I realized while playing Ikaruga the other day that even though it was designed for a next generation system, the underlying concept of switching colors to defend yourself against light and dark bullets could have been done on just about any console.
Any console, that is, but the Vectrex. GCE's portable system was capable of many things, but I couldn't imagine playing a game like Ikaruga, which is entirely dependant on the player's ability to recognize onscreen colors and react accordingly. Sure, you could dim some of the onscreen objects, but the simple fact is, they'd all be white... some of the bullets would just be less white than others, creating no end of confusion.
Can you think of other examples where a game just wouldn't belong on a specific game console? Try to avoid obvious examples where the game in question is so technologically advanced that it couldn't be done on any of the classic systems. Instead, concentrate on each system's specific weaknesses and think of a game that would exploit those weaknesses.
JR