I liked how many characters you have, even if most are locked away to start. The upgrades are nice, though trying to read them to pick one during combat can be a pain on the first playthrough when not familiar with what is offered. The geometric shapes worked well, though early one some enemies looked a little too similar to XP. Later on it made sense to have a sort of Mimic like enemy that is close, but early on it was unexpected. I suppose with the geometric shapes there are limits and things will look similar. I got to just avoiding heading directly for them and let them get attracted if I wasn't sure.
I played at the default difficulty. I managed to beat the Mega Boss, earning 88 Star Tokens, and 19 Achievements. I found this game to be fairly easy. I was not sure if there was an end to the run and was debating how long to keep playing. The Star Tokens allowing permanent upgrades, and unlocking new characters with achievements does add a bit of replayability, but the first run was so easy that I'm not as interested in a replay. It feels like rather than powering up more, I'd need to do things to increase the difficulty. Well before the end I lost any concern with losing, and was not having as much fun due to the lack of challenge. I don't play a lot of chaotic fast paced games outside of jams, so I was surprised at how easy it felt. I expected to lose a few times and unlock things before being able to get far. Play balancing can be tough, so I don't know what the best advice is here. The main point for me is that if I'm already easily winning with the default character and no upgrades, then unlocking the upgrades doesn't feel very rewarding. You spent the time to create them and the systems to unlock them, adding replayability, but the game balance takes much of it away, at least for me.
I did enjoy the early game, and liked seeing all the options. It wasn't until the difficulty dropped that I started to tire of it, and debated how long before ending to rate and write my feedback.