The gameplay is fast and fun, movement is smooth, and the mixing and matching of spells on your hands, while takes a bit getting used to works pretty well. I've only encountered one minor issue on flatscreen mode where the exit direction of the shopkeeper's room didn't match the compass (facing the exit it points to east but the room exit is to the north). For the blue fire floor, I had a feeling that it might damage you, but after falling in and seeing no damage feedback I thought it was safe after all - until I got killed by it, so some feedback that it hurts the player might be good. Similarly, for spells with cooldowns and charge ups, an indicator of when you can fire again/how the charge up is going would be nice as well. This is minor, but for Viridian orb it also seems like the projectile spawns pretty far away from you.
For VR (played on the Index), I did notice a couple of issues. The main menu "sticking" to your face feels weird as a start. On the right spell wheel I was only able to select Viridian orb and Scatterblast, though the left spell wheel worked fine. I was seeing both a white hand and full body, and the option of turning full body off/on didn't seem to do anything. Also sometimes I wasn't able to jump out the blue flame pools in VR, ending up getting stuck in them while this wasn't really an issue in flatscreen. Enemies and general objects also seem to block the raycast for using menus, making the menu operate when you die and get swarmed difficult. And while I have a decent PC, it felt pretty demanding on performance even with everything but Shading Mode/Lit turned off (even had to go Unlit in the end).
For my more objective findings, getting all spells dumped on me was a bit daunting at first. I'm not sure what kind of progression you've planned, but I'm wondering if something like starting with only one spell per color (even random for each run) and then unlocking the rest later would be something worth experimenting with. Even with randomness rooms get a bit repetitive at a certain point - maybe something like multi-wave spawns could spice things up. Similarly for end of room upgrades, I'd like to be able to choose one upgrade between multiple options as with only being offered one feels "I'll take it I guess".
Specifically for VR control, I'm personally not a fan of having to use thumbstick press as it is the mother of drifting sticks. It wasn't a big issue changing the mapping in SteamVR, but would be nice to have an option to open the wheel without it by default (even if it removes the ability for you to move and turn during). I understand it's the curse of limited buttons, but I noticed Grab wasn't being utilized so maybe there's a way to map things that leaves one facebutton free for it on both controllers.
Overall I think the foundation is solid so far and with enough polish I could see myself going back to this game every now and then for a few runs.