This is very cool! Coming from a beginner, it might make the first few games easier if you added an extra setting that would start the puzzle with one or two numbers already filled in (like a typical sudoku), as that gives a natural starting point. Obviously, it may not be needed if you mainly develop this for yourself :)

I believe in the Puzzle I attempted, the solution was not unique: at the end, two numbers could be placed interchangeably (in my case, I could switch around all "1"s and "4"s and end up with just as valid a solution - that is, of course, unless I missed something :)

Very cool little puzzle, thank you for sharing!