Played through quite a bit of the game so far, it's fun and surprisingly polished. I do have some criticisms/suggestions since I see you're working on updates.
The only real long-term goal right now is to max out all upgrades, which is a bit hollow since you'll exhaust the game's content long before that point.
The apparently endless(?) floors runs into performance troubles rather quickly, around the time the second large enemy starts spawning. By the time the third enemy was spawning I was afraid the game might just lock up entirely.
I think separate stages with limited floors could be a way to ramp difficulty without overloading the spawn rate. Add a stage boss and you've got a goal, plus the added difficulty/pressure of clearing the stage before your battery runs out.
Additionally, it took some time to realize that my equipment was leveling as I dug deeper. This element isn't particularly clear and in general a way to check current stats (maybe with the home button) would be welcomed.
Not sure how much time you and Dave want to put into this project, but I really think it could be among the Playdate's killer apps with some more content and polishing.