Thanks for the reporting the problems. I also feel the enemies are spawned too fast that the player may have no time to prepare. Probably because i have played it so much time so i felt it normal. I will fix this later. About the bug you mentioned, i don't really get it. Can you explain more about that?. And i will add the tutorial.
And maybe you should know this. This game is my entry so it's a once-developed game (i hope you understand what i'm trying to say), so i will improve all of the missing feature in my next game.