Balance, performance and logically patching things.
It's not out yet i understand that but it has ways to go, for instance the first available Biome is MUCH harder than the others because of lack of cool water (you have a fixed 2 cool steam vents and volcanoes wich you can't really tame early on, plus teleport gets you no more water).
Solar pannel need fixing yes, but the problem is once again power wise you don't get that many options, coal is very limited due to sheer size of asteroid, ranching is an option of course. But i feel like recently Klei has been patching things without adding the counterweight, one of the more obvious patches was the food one. Yes it was overpowered be we were not given new tools (early,mid,end) to deal with food preservation.
I love that sand is much scarcer and i finally have a use for Chlorine vent. In the same way i'd love to have uses for everything in the game. I feel like there are too many metal volcanoes, we should have the whole range of volcanoes arranged on the planetoids including some maybe new ones to cover everything in the game.
Performance... this is the MAIN problem for a lot of players, i understand the technical difficulties behind it all but we still need better performance.
Rockets, i've said this from the start and i'll say it again i dont like anything in the new rocket system, not a single thing about it. It's just my personnal taste