Great gameplay and idea! It's also incredibly addictive. Balancing when to take hits and when to heal and attack is interesting. Random start weapon mixes things up too, but might diminish the value of purchase options at gravity well a little, if you start with a "good" one.
Every once in a while, I stumble onto a game that fits perfectly with Pico-8, but that I wish I could play on Steam/PS4. This is one of those. Would be great to see it expanded/ported, but glad I got a chance to play it. Well done!