Well there is a lot to say but it is a good beginning.
Here are the things you could improve:
-the character slips too much, we might think the floor is made out of ice
-lifebar is too simple, you could customize it (round border, wide outline, texture...)
-wall jump mechanic, usualy in games the wall jump is more like a bounce to get to higher and further platform , it cannot makes you land higher than where you jumped, here if we hold a direction and jump we can just climb every wall
-graphic style, too many different style of assets, walls and portals are too detailed compared to spring platform and robots, also flashy colors backgrounds attacks my eyes
-the bullet come from player origin and not from the canon end
-when platforms move horizontally player don't follow the movement
-too much air control, the goal of a platformer is to anticipate the jump (and make some small adjustment mid air), here you can go anywhere you want during the jump
-robots can kill you even when they are dead when you touch their claws
I know I am rude, but it is your first project, and learning take time, don't be upset again gamedev, there are also good points:
-I like the character animation
-Clean and intuitive UI
-lot of levels