Thank you for your feedbacks!
Yes you're right, it's very hard :p. I managed to finish it in one day (I had to do it for test purposes).
But that's not normal that you keep stuck in level 3, I wonder if you are not facing a bug...
Concerning the sound, I've had enough of working on this project so I've decided to keep the sound part (I've made some test but that's very hard to set up weapond sound without to break the ears of the user).
I don't know if I would find the time to update the game and fix the differents remaining bugs, I'm really busy with commercials projects (and when I find time, I work on Unity which is really productive).
I will use PixTudio again in my free free time, for pleasure, not for big project.