the key gimmick is after the first two gyms you decide whether you want to do the east half or the west half of the state, then once you beat the championship the routes open up to do the other one

the east half contrasts apocalyptic flooding in the past with contemporary irrigation and dam projects

the west half contrasts lush greenery and urban development with apocalyptic volcanism in the future

yes the legendaries are kyogre and groudon