Thank you for playing the newer version of the game instead of the official one!
All of your points are good and made me research few things, even made me research few things.
Opening the game at first might take around 10 seconds while using an HDD because of shader compilation and a memory allocation (the game wants to load 1GB of assets to your memory right away). About shaders, I will try to look for some unnecessary variants and remove them. About the memory allocation, the game should load the scene after clicking the "Play" button. I don't know why isn't it doing that way. I feel like there is some direct reference to the scene. I will look at the code and try to fix that.
About the game balance - The game works in a way that rats spawn at you within waves. Each wave gets bigger than the previous so with each wave, rats cause more and more chaos. Thanks to your feedback, I've noticed that after some point (like 7 rats and more) the wave gets so big it's gets a bit too hard to win. I will try to balance that a bit better.
And about pushing various objects by moving at them. The last time I've tried that, it caused so many issues and bugs everywhere I've decided to not do that almost immediately. For example, small items could go through the floor If you'd go over them. I might try to search whether there is a way to handle that properly but I can't promise anything.
And for sure I will review your game!