Good puzzle, marred by crashes & annoying controls
This is good enough that I've spent a few hours with it while on the subway. Unfortunately, it crashes every now and then - probably once an hour on average. Also, the control implementation is just a tiny bit off. Every so often it'll register a tap when I mean to drag. In this game that can destroy your perfect score, which is very annoying. If not for those two issues, I'd give it four stars.
It could easily be a five-star puzzle game. To get there it would need a way to mark squares as certain, or even a lockdown toggle so you can't change a square by accident one you set it correctly (a mark for "definitely wrong" would also be good). On the twisty 15-unit grid, I waste a lot of time reviewing previously moved tiles because I don't recall if I actually moved them or not yet, and marks or locks would fix that. It would be a nice but lesser improvement if you could turn off the energy source - the bright color can be quite a distraction early on.