I wouldn't mind a theme park within a sandbox. Kind of best of both worlds. That I could easily be happy with.
Exactly, why it has to be only one or the either? Taking inspiration from good ideas & elements of both seems ust logical to me. The GTA/Assassin sandbox console games people keep bringing up mix it up however they want, including both linear story quests along with RPG influences, sandbox elements and anyting they feel like would make the game world seem more alive & dynamic yet with memorable characters and events populating it and variety of activities.