Yeah, Ripe Seeds (Plant Castle) is my favourite track in the game.
Overall, Belmont's Revenge has the best soundtrack on the original Game Boy, IMO... I honestly can't think of any game with better music. Maybe Seiken Densetsu, or Link's Awakening. Or Castlevania Adventure, obviously. But no - Belmont's Revenge it is, at least for me.
EDIT: Well, there's always a possibility that Sunsoft did some spectacular soundtracks for the GB, but I can honestly only remember the music in the first two Batman games, which were very good, but not as good as in Belmont's Revenge.