Just trying out the beta for the first time (played Alpha as well).
Two UI issues that immediately hit me:
1) In the planet screen, there is a button to buy the thing you are currently working on (near the bottom right) and another buy button for the thing you are highlighting (near the right middle).
I found myself constantly going to the middle button...seeing it was grayed out...then realized I meant to hit the button the bottom.
2) No mouse scrolling yet. I'm sure its something you guys are looking at, but I won't lie its a huge turnoff for me. Would really keep the game moving if I didn't have to use arrow keys all of the time.