Robotnikland does fit the zone, but I can't help but think that the name would put the game out of chronological order. In Sonic Adventure, Robotnik said he was planning to build the ultimate city, which he'd call Robotnikland. With that in mind, I don't think Robotnik would name his amusement park Robotnikland if he would later plan to give that name to his city. On that note, I also like the name Sunset Circus. I don't think it really describes the thrill or scare aspect of the zone (considering the Robotnik faces on the tiles and the giant roller coaster), but it's still a neat name, and it fits in with the other Sonic zones that were similarly named.