The UI is "ok". But certainly has room for improvement. (Both in process and in execution)
If you're referring to PC, sure it isn't exactly tuned for mouse and clicking, but it works more than fine using WASD E/tab.
Honestly, though - that's just a bad way to make a PC interface.

(Also, maneuvering among the stars in the perk constellations, with WASD, doesn't work quite right - it's not always obvious which direction you'll move with each keypress. And the mouse maneuvering in the same place has issues, too. That whole section could use some work.

)