Hi there! Definitely a joy to see more incrementals like this that don't force a timer on you! I do agree with everyone's sentiment that it is a bit slow, not the level clearing per say that feels pretty good, but more the I am getting new things aspect of the game.
For example having your 1st item in first shop tab you see unlocking feels pretty demotivating yup I definitely saw the other items that unlock in the other shop tabs, maybe show those tabs first instead?
I think part of the feeling could also be alleviated by having some kind of notification pop up or highlight or something similar when you have a new upgrade or item you can purchase in the shop to show the player there is something new for them to take a look at.
Overall though with a few tweaks I can definitely see this being a really fun time, great work!