Congratulations! Game dev was the story of all of us. : )
I like everything about this game: graphics, animations, sounds, music, challenges, etc.
This game can pleases the 3/4 types of players:
Achievers: what I achieved
Explorers: explore mysteries,
Killers: detonate and blow everything up
Only for Socializers that have less stimulus
What could still improve is Level Design.
You could make about 3 versions of the game just combining and repositioning elements.
The "level design" can be better understand as "progression architecture".
This could be better elaborated if you could work and focus only on this.
For example, the first challenge/phase could be much simpler and faster to complete.
And next mission, a little more slower and more difficult.
And without many elements on the screen.
You do not need to spend all your ammo at the beginning.
The richness of elements, details and variations can appear gradually to surprise the player.
The complexity should gradually increase.
After the player has experience with the game, all can be more free.
Much players also like to have a "checklist" that produces a sense of progress.
Like finishing the level with all items found or 100%.
And a notion of duration: in universe or galaxy 1, there are 10 phases, in universe 2 there are 10 more phases.
And I complete 10 stages and 15% and found 10 weapons.
That is, keep visible the progression and achievements. How many levels have I complete? How much have I progressed? How much more powerful did I become? What conquest and exploits can I show to other players? What is the return of playing time?
In this game you already have all the elements you need.
The most difficult was programming, drawing , animation and elaborate the idea and universe of the game.
Now the success level of the game depends mainly from only: sequence and reward.
The player who plays a level must be curious to know what the next one.
Like know the rest of the story or the end of the film.
And I believe the game has not yet achieved that at a good enough level (for most players).
And there was little left to get.
In a game there are several progressions: narrative, achievements, difficulty, speed, amount, power, etc.
The video that best illustrates the "progression of power" is this: The Art of Screenshake
youtube .com/watch?v=AJdEqssNZ-U
This video helps like have new eyes to compare amateur games and professional games.
If you still have patience, you could invest more in this aspect.
Asking players and game devs won't help much with Level design.
Players are best to test and modify what you have already developed.
What can help is to talk to those who work with Level design.
Or look for inspiration in other games that has this as the biggest quality point.
But, if it is no longer possible, that learning can be left for the next game.
Also, if you haven't launched, would also be good that you look for a publisher.
For example this: thearcadecrew. They are focused in retro games.
Can help you with marketing, port the game and published on all platforms.
If they are not interested in this genre game they can recommend something.
Anyway, good job. I can even suggest these ideas, but I wouldn't do better. : )
