Create your own artwork. There’s nothing wrong with using the basics but it gives the game more of a personal look if the creator takes time to make their own.
Add sounds. Though I do have my flowlab tabs on mute, it’s still nice to have some sounds, I think there is a library you can pull from.
It’s a very basic platformer. Nothing wrong with a good platformer but if you are going to make one you should customize it instead of just having water and spikes as enemies add other things! Or you can make falling blocks or invis mazes
Why the floating blocks. You can get away with having some blocks that are floating but having a bunch of floating blocks for no reason is just annoying and distracting. If you dont want to make them solid but also make them not floating, you can create sprites on the background layer that look like dirt or something.