Thanks for your advices !
You are absolutely right about all of that, if you want to know, 1 hour before i published the game there hasn't the possibility to change the canon ship, because at first at wanted to do a lot of UI things to know i you have ammo, where the canon is targeting... but the UI part was very complicated to me so i decided to give up that.
And for the big boat, I knew that some people wouldn't understand. I thought that making it flash would be enough. I hope it doesn't discourage some because the majority of the work was done on the "platformer" part, but even then, initially, I wanted to do something with the UI.
But to be honest, I don't know if I'll go any further with this game. It was a great experience for me, but because I'm a lazy person and I do everything at the last moment, I had to code very messily, and I don't feel like getting back into this mess, haha.
But thank you for your comment, it's very helpful!