Cool li'l thing! I like how you've incentivised moving around pieces, that being such a standard problem of tower defense games. There's probably more that could be done with this in many directions, as it definitely gets stale after a few rounds, but there are loads of possibilities (chess-themed and otherwise) should you decide to add more levels, make the current level expand, etc.
Great work! It's polished for a more experimental Jam title and plays pretty well! Gameplay-wise, I'd recommend at the very least limiting where players can move their pieces or allow a bit more leniency with getting to spots that should in theory be invalid to place a piece in if they player is really close to being able to. With either solution, you'll be more clear with where the pieces can go system-wise, which doesn't seem like as much as a focus, and, currently, is distracting from the interesting of moving them around tactically (more strict in placement, or more lenient in movement, does that make sense?).