8 - GC - Metroid Prime (+)
7- - SNES - Super Metroid
5 - Wii - Metroid Prime 3: Corruption (-)
5 - GC - Metroid Prime 2: Echoes
5 - GBA - Metroid Fusion
4 - NES - Metroid
3 - GB - Metroid II - Return of Samus (-)
@KylieDog: The format is well-established, if not perfect, so topocs tend to work and do come out with a good answer. One possible protective measure is a rule that the same game can't recieve both minuses.