Hard and fun
Fairly good game, enjoyable, with the difficulty level scaled to a player who knows how to manage money.
It took me 3-4 attempts to get it right.
Always get the blue 'W' upgrade after the miniboss.
Keep you acc as high as possible for the first 2 levels, don't buy anything after lvl1, full firepower after lvl2. If you go for firerate your accuracy will go down and you'll get less cash later on. After lvl3 - firerate lvl1, then sell it after lvl4 and buy full firerate. max the armor and drone( I prefer spreader and autoaim) with what you have left.
Mouse+Space is vastly superior to arrows.
btw, the two last Bosses (not minibosses) are way too easy. 'Scorpion' ( I think) - you need to fly in the right spot with drone and the boss dies almost instantly. The last one - you don't even have to move if you have about 20%health left.