Currently after some progress there is no point in merging new runes because energy regeneration is always 1/sec and player can't do anything with it.
It took few hours of just sitting and waiting to unlock all 10 stages, which is silly.
I think I have perfect solution for this complexity problem!
Since every stage requires exponentially more energy than the previous, my suggestion will not make the game too fast also, since it gives additional linear growth.
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THE SOLUTION:
Amount of energy regenerated per second should be equal to the ritual number - amount of the solved pazzles.
At the beginning nothing is solved, regeneration 0.
So, you solved the first pazzle and got the required number - now it's ritual 1 and 1 energy/sec; than after the second solved pazzle it's ritual 2 and 2 energy/sec, etc.
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Suggestion: adding below the portrait total amount of energy to unlock the next stage and how much left to make progress more visible.
Suggestion 2: making 4 cells instead of just 3, so you can get "+1", "+2", "+3" or "+4" (with equal probability), as others mentioned sometimes it takes plenty of time to get "1/2" cell for the solution.
Or "+1", "+2", "x2" and "x3" - that will be even better, I think.
Well, even without "x3" and just 3 cells "+1", "+2" and "x2" everything is going to be much faster.
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I liked the game and I hope my suggestions will help!
I have plenty of experience with calculating algorithmic complexity and the speed of the progress, so I will be glad to help with the balance. :)