The grind in this one is real. The devs seem to have made grinding much harder by making replaying maps giving significantly less gems. Stopping meaningful progression to farm the same maps constantly just to get one upgrade is simply not fun. The enery system makes that even worse. I don't really see the point in an energy system an off-line game anyway. It's off-line, I'm mean to be able to play when ever. An energy system cripples that, and penalises grinding... Just pointless.