Today I finished the game despite some little annoying bugs.
My personal rating
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Flawless version: 8.5 of 10.
This version: 7 of 10.
Improvement could be for instance
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- the boss of each chapter is to easy.
- the end boss of the total game is to easy.
- aliens do not stuck weirdly
- a better distribution of health power-ups.
Sometimes in no time 2 or more power-ups are showing up, despite your health is at maximum.
- skill levels like novice - amateur - professional
The list does not have to end hear, perfection is as usual impossible.