Nice music. Good use of generator-boosting upgrades to give the player a little choice in their next step to greater point generation. Showing the next unlock's condition, and the subtle "fill this up, something will happen!" bar near the echo count all provide incentive to keep playing in the early game.
By about the Amplifier unlock point it starts to drag a little, and by the Harmonizer unlock it feels like the player is waiting for ages for extremely minor incremental gains. Active play is no longer valuable at all - exponential click-boost costs mean that the value of clicking has become negligible, and the increase in echo per second for purchases that take two minutes or so of idling is also barely noticable. That "2 minutes" stretches as the exponential costs go up, getting longer and longer... It feels like the post Harmonizer pacing is designed for "leave your computer/phone for two hours and check in later" style play. Maybe that's the goal - Trimps and Kitten Game make that work - but it occurs simultaneous to hitting the "my next few purchases aren't really going to make much of a difference, I've gotten to the top of the 'linear vs exponential' power curve these games have already" point, so engagement suddenly drops.
My game also didn't actually save, so when I checked back in after a little less than ten minutes selecting 'continue' started me over from scratch. I didn't clean my cache or anything in the interim.