Opa Opa being too obscure and uninspired is hogwash. Consider that Fantasy Zone has appeared at the Arcade, on the Sega Master System, MSX, Nintendo Famicom, Nintendo Entertainment System, TurboGrafx-16, X68000, Sega Saturn, Windows, PlayStation 2, Game Gear and Virtual Console.
Then consider that Space Harrier exists in the same universe as Opa Opa, that games such as Planet Harriers and SA2 featured Opa Opa as an unlockable, that Shenmue has a capsule toy of Opa Opa, that Samba de Amigo and Bayonetta feature the Fantasy Zone theme... the little guy is totally a Sega All-star!
I'm not against Opa Opa, I know it's fame, but I think it just doesn't fit in a game like this.
Gilius in a "flistons" type of monstertruk with bones would have been a better choice. Hoping for DLC right now