I think you used the wrong settings when setting up your project, unfortunately the antialiasing looks very bad when the game is scaled up... You can fix this by either changing the scale mode of your project or by changing the interpolation mode on your scene's nodes.
The design is very simple but it lacks some of the important features of a platformer like coyote frames and jump buffer that would make the controls feel much smoother. Some of the platforms are not very clearly delimited (the edge of clouds aren't solid for example).
Despite the flaws, it's pretty good for a very first game, it works well and it's quite fun!