Okay first of all, I beat the first 6 levels before writing this. Most of these are my own opinions so there might be something that will not work for other players, but I tried to think the game as objectively as possible. Like I previously (maybe) said, I liked the idea and enjoyed the gameplay, so my comments are mostly about adding more visual cues and tweaking some small things.
(I also posted this without reading the previous comment so there might be some overlapping things)
GAME MECHANICS
- Ability to drag doors instead of clicking would be more intuitive to me.
- Some kind of high score system since currently the game doesn't remember what you got from separate levels.
- Is score really needed if we already have time counter? It can make the game more stressful to see your score slowly decreasing.
- Like someone already said, door position shouldn't reset every time you shoot but only if you choose to reset it.
- At least once, the ball moving horizontally and just stayed there jumping till infinity. It would be good if the game detected this and informed the player somehow, like "your ball is stuck, reset? " and a reset button. Or a mechanism that will push the ball a little when this kind of situation occurs. I'm not sure if you woud like to decrease the jump force over time or keep it constant, but you might want to try out both and see which one works better.
DIFFICULTY CURVE
It is possible that some people can't figure out certain levels and will get stuck, especially when not being able to collect all the stars. I think a usual way to fix this would be to make collecting stars more voluntary, for example adding each scene one star you must collect and to make other additional. Then, you could limit possibilities to proceed within different levels by giving certain star thresholds, like after the first 5 levels the player should've
1) beaten all the first 5 levels by collecting the main star and reaching the door
2) collected at least 10/15 stars
Requiring that the player always collects all the stars may be too much and you lose an opportunity to put any hard stars for more advanced players.
GRAPHICS
I like the graphics as they are, but the quality of them should be increased to lure people in. Published games usually have a good resolution but now it is kinda fuzzy in plazes, e.g. the player ball could be more hd like in the cover image. Might be about the game engine settings?
I would add some pretty highlights, like on the cannon where the ball is in. A small not so neccessary change but would make the game look more satisfying.
Also some kind of implicator when shooting that shows you the force used to shoot the ball. Like an arrow that will be bigger when the velocity will be high and smaller when don't. This would make gameplay easier after the player has figure out how fast the ball will be shot by analyzing the implicator.
PLATFORM
I feel like this has the most potential as mobile game, since most of the casual gamers are on that platform. It depends if you're going to make it free-to-play or not, since on the other hand people don't really spend money on Android games. Publishing in Steam also costs quite a lot, when in Google Play for example you must pay something like 25$ to put up your developer account and after that you can publish as many games as you want for free. There are a lot of other things to take on account too regarding publishing, like making a mobile build is a bit more complicated, but you should at least decide whether your main goal is to just publish your own game or actually to profit with it.