I'll be honest, as good as the game is, on 3-X I get so distracted by the coloring of the level, it really throws off my timing and concentration... I'm sure that's just me though, still its a bit annoying, but its something that I can bear with if it just means beating the game and being able to hear the full song. >w<
Mmm, since this is similar to things like the cookie-clicker, I would like the game to be responsive to fast clicking. I only say this because clicking manually has a short delay until the game responds to the clicking, being that I could click maybe 10 or 14 times within a short time frame and the game will respond to maybe three-quarters of it... I'm not sure if its just me that is getting this, but its something that wouldn't hurt to look at right? ^^
I'm picky about how things are set up (maybe I have OCD), but anyways I would like to be able to rearrange my boards and make it look all nice and pretty... Other than that just like many other people have suggested, a way to optimize the game. I'm patient, so take your time.
 "Death Run 3D"){kind=icon}
 "A Dance of Fire and Ice"){kind=icon}
 "Idle Mine EX"){kind=icon}
 "Idleplex"){kind=icon}
 "GemCraft chapter 0"){kind=icon}