good start, but the cost of planets scales way too fast later on, leading to having to redo the same easy planet several times. I assume you plan to have upgrades to get more money later on, but you probably also need to increase the scaling for the energy upgrades later on.
At prestige level 8, the game becomes incredibly laggy for the smaller planets.
I assume the game isn't balanced up to that level. I always found it weird how idle game demos don't have an ending. Just a point where it stops being fun.