Jurassic Park for Sega CD!!! It wasn't PERFECT but I still loved it.
The SNES and Genesis versions would be nice, too. None of the sequels were that great, but I'd still buy those. But JP for Genesis is 2nd only to TMNT IV for SNES for games I want most on VC. If Sega CD games came up, Jurassic Park would top the list.