Thank you. I had trouble gauging the difficulty, so hearing about your experiences is really good- I know the game (at least, in its current state) can get repetitive quickly, so I notched up the difficulty on purpose. If I start doing more to it (more shop items, more types of obstacles etc) then I'll tone it down.
I did have a wave/round counter display on the screen at first but then removed it. I think I will bring it back next time.