Hi felix. I played the demo and nearly completed level 3.
It seems to be a cool concept, and it's obvious that the game is a labor of love.
As a dev, I'm very impressed by what you have so far.
I really wished that I would have loved the game as a player too but there are some things that turned me off.
With some polish I believe you can have a very nice game here.
The biggest issue I think is the platforming/jumping.
Most puzzles were easy to figure out but hard to complete due to the platforming (this can be detrimental for a PUZZLE game).
You're using a circle shape to represent the player so it's very easy to get stuck on the corners of platforms where the plazma being is not falling but you can't jump either or move sideways towards the top of the platform.
I think you may want to try another collision shape (such as a rect with disabled rotation) or somehow allow the player to jump in such cases.
Also, the jumping is not as precise as I wish it would be. It doesn't matter how long you hold the jump button - the plazma being jumps the same height.
These may seem like minor gripes but I failed so many times due to these two issues which would probably frustrate average players who don't have as much patience.
The control scheme is a bit complicated which is fine but I think it would turn off casual players instantly.
One suggestion I have for this is to make the 'shooting' mode (E key) accessible via the mouse wheel and perhaps remove the 'shift' to accelerate key altogether (from what I've played so far there doesn't seem to be a reason why you wouldn't want to be running all the time).
There are some other minor gameplay gripes but overall it's probably miles ahead of most other Love2D projects in terms of its commercial potential.
I like the flies and the dentures on wheels you have in some of the levels, they seem to give the game character.
The first puzzle with the fly which is blocking your path is a bit cryptic though, my first initial thought was to shoot at it with the E button.
Keep it up, nice game overall!