I hope there's more environmental variety in the levels this time. Most of the levels in the first game were either grasslands, rivers, or caves, the only relatively unique ones being Volcano and Rainbow Cloud. I'd like to see some more unique biomes like deserts and snowlands. Gamexplain also speculated based on the oceans looking clear and the design of the new version of the Zero One (Zero Two? Whatever the hell they're calling it now) that it should be capable of going underwater, so an underwater section seems especially likely.
Speaking of the Rainbow Cloud though, I liked how they made that level essentially a "boss" level with Mew in the original. For those that didn't play the original, basically you spent the whole level trying to get Mew's picture. It had a shield surrounding it that interfered with your camera and you had to get rid of it by throwing Apples or Pester Balls at it in order to get Mew's picture. It also had multiple phases, after three hits the blue layer of the shield flew off and Mew started flying off camera quicker, then after another three hits the yellow layer flew off and Mew started chasing after the shield and you had to hit it one more time for it to turn around and pose for a picture. I'd like to see more "bosses" like this, and since there's a LOT more legendaries since the original, they can afford to do more of these. Maybe they could go as far as one after each regular level.