I wouldn't say each of the main cast getting their spotlight is something that unique to Nekketsu (Battle Shonen) manga though. Ring Ni Kakaero, Kinnikuman, Saint Seiya and Sakigake!! Otokojuku did so long before OP did, and did so in a manner more evenly spread out than for the main cast in more recent OP Arcs, with several crew members having been shafted for a while during the timeskip.
As for the world building, I honestly wouldn't say it's that good. It's creative, sure, but a lot of elements feel disconnected and unbelievable. For instance, the village Luffy grows up in is just outside of the giant Goa Kingdom as just its own independent piece of land, something that doesn't really make any sense, and there's no real reason given as to why the Grand Line islands all have their own unique magnetic poles to create ecosystems completely different from each other and completely unconnected (it may have something to do with the implication of the OP world having several moons from the Ohara models, though that's complete speculation right now). Also, for a series that gives constant focus to individual kingdoms, nations and political intrigue, the individual politics and customs of the majority of nations is quite lacking in its exploration, Skypiea and Fishman Island being the only major exceptions. OP's world has good concepts, but could use a lot of improvements in its execution.