Here some honest feedback on your game. So you don't need to hold back judging my beta...
In options menu: What is the difference between back and menu? Both seem the same to me. And first I tried 'exit' but it closed the game despite being in some sub-menu.
The music in main menu stopped after a while. Seemed strange to me.
I realy like it that you introduce the 2 characters at the begin.
The increase of difficulty seems okay. I think the first boss is too hard, since I always have to think which of the 2 guys I will move with my keyboard. That will require a lot more skill in controlling these 2 and that will only happen by playing it often.
But once you solved the puzzels the replayability is not too great. So players might not be up to build it up to that extend in the first level.
Using slow mode would make it easier, but still the boss has several new techniques for the player to learn. IMHO too many for 1st level:
1 Moveable shields
2 Direction of enemy fire changes over time
3 Change of fire pattern (not clock-wise but anti-clock-wise.
4 Introduction of random change of fire pattern (clock-wise, anti-clock-wise, clockwise, clockwise, anti-clockwise and so on)
5 maybe increasing speed of the boss. I am not sure about that, since I was put under stress.