great game. i had no legitimate complaints. other than maybe not being able to see stuff way below me before deciding if i'd commit to irreversible actions to get down there.
would like more varieties in a sequel. the typical desert/frozen/etc. biomes.
some more abilities too. which might seem hard from a level design standpoint since it's easy to put stuff out of reach till you get an ability, but not easy to make sure there are enough coins accessible to get to the higher abilities no matter which order you buy the abilities in. i could see from the start that must have been a complex problem.
solution for more abilities would be to do it in tiers. you get these three abilities and then after that it unlocks another set of abilities. that forces them on a slightly linear path.
more variety in elements. bouncy pads, spikes that fall when you go under them, portals.
also you should have it so multiple players can play together at the same time. have gear that you can get and some materials you can gather so you can craft them into armor and weapons. a pvp arena for testing out your new gear and maybe some dungeons that were less puzzley but more about cooperation between players.
then all you'd need were some hubs where you get quests for going out into the world and also it shouldn't be level based, but rather open world where you could tackle things in kind of any order like talos principle but more like world of warcraft. it needs overarcing stories as well. one big one then one medium one for each zone, then smaller ones for individual quest chains.
also i don't like how there were no pets.. and it's annoying that you're just this one guy there should be multiple classes and races.