First one is that I found myself not even noticing that I rank up or get some progression on challenges/ranking and etc. It does not have any satisfying sound that would be a "reward" for progression in the game. So my suggestion is adding some visual+sound effect on ranking up.

Second is in Tech Tree, when you learn or research something, it doesn't highlight it in the bottom menu, if you're new to the game, u probably won't even notice where that new stuff is or what building you learned, and adding some marking, shiny pointer is one of the good QOL experiences