I think there really need to be some guidelines on the game start menu about the sort of RAM requirements to get playable performance out of certain Galaxy sizes and number of players, just to manage people expectations.
I'd agree that to a new player GC3 is not the most approachable game, some good tutorials will fix that.
There are other bug bears I have like synthetics getting planetary events to do with food and organic diseases that makes no sense mechanically or flavor wise, and I don't think they have any intention of fixing that prior to release from what's been said.
Mostly though I think they need to look at balance, typos, graphical glitches, crashes, and UI issues.
ultimately I'm hopping I'm underestimating how much further along Beta 6 is from 5.3 in terms of these things, but while the currently published bug fix list looks promising the proof will be in how it plays.