I'm sorry to say this, but I did not enjoy your game.

First try to improve the graphics. If you do not have a graphics program, you can create simple sprites within Unity. Therefore go to the project window and press right mouse button > create > sprites. With simple graphics the game looks much better.

Also the level design is not very good, the enemies are placed in a way that makes it very difficult to get the keys. In fact the only way to get the keys was to pull the enemies away. This was the most frustrating part of the game. A simple "maze", where you have to find the right way through a lot of enemies, is in my opinion the better choice.

Otherwise the third level is not playable and the button "How to play" shows nothing for me.

Please don't be too angry with me when I criticize your game. I have tried to give you constructive feedback so that you can improve your next game.