All is good! :) A game can not be a fit for everyone, but still all feedback is important to listen too. Also, i have only had about a total of 1 ½ weeks devtime on Zentaisen due to the competition and other stuff in life.
When you add new features and try them out, something else can feel less good and so on! Leveling up right now only raises the Max HP, and with money you can buy Weapon powerups such as bullet power, ship speed, extra lifes, bullet spread etc. The first version just threw you all the upgrades directly and i thought that everything just felt "too easy" almost.
But still, it needs to be balanced to not make it feel boring or lengthy in a bad way.