Beat the game after a few attempts. It's pretty fun and the writing is very good. I wish there were more lore events even if they didn't directly provide upgrades, but it's certainly not a serious obstacle to the game being fun.
My first run-through I assumed there would be some benefit to going into the portal room earlier instead of grinding, and since I had started with the water spell and rothearts are resistant to water and common I figured the boss was likely weak to water as a game balance thing which turned out to be correct. I entered the portal room immediately and killed the boss in a pretty near fight. It was pretty disappointing when, after barely beating the second boss in a similar fashion, I died to a breath-taker on level 3 and found out when starting over there's actually no reason to ever enter any portal room early and a lot of reason not to.
Merging spells is a neat mechanic, though at first it was a little annoying you can't ever merge your last spell slot, I think it's actually kind of a neat mechanic since it garuntees the basic spells also see some use. If the game continues development, the current final boss's smelt move is nuts and adds a hefty dose of rng to the game since presumably the next floor with have exponentially more ridiculous enemies as always and losing the wrong two spells could definitely ruin your whole run. Plus I think it bypasses standard accuracy checks (i.e. light doesn't effect it) but idk for sure.
Finding out what merges do through play is a fine and quite traditional take for that mechanic, but I do wish they were a little more balanced. Freeze's damage and accuracy nerf makes it more of a (unreliable and short-lived) control spell than a truly offensive one so you'll really stuggle until you replace your lost offensive spells there, whereas Fireball is a straightforward upgrade to Fire and the accuracy drop is much simpler to play around than all of Freeze's baggage. Ray of Hope is super good so maybe it makes sense that it's hard to recover from losing a Light spell for a pure offensive option, but it's still kinda weird. Water+Mend=Imbue is still probably the most difficult to recover from I think. When I first did it it was frustrating because Imbue seemed useless compared to my main damage spell and the ability to heal, but now I recognize that it can be one of the strongest spells in the game. There are easier ways to get it, though, so it's still a little weird.
The enemy on floor three that eats your shards is really annoying. It+Breath Takers just seems like a much more brutal combination than anywhere else in the game, even if the stats on those enemies themselves aren't actually that high. I guess it's probably just to reward fast combat builds and punish buffing, which is a good idea, but it still is a pretty steep jump in tactics even compared to between floors 3 and 4 (Forgelings seem like they should be a bigger deal, but I've not had too much trouble with them).
If you use Imbue on the Void Master it seems like absorption and weakness should probably cancel out but they in fact do not, presently. Also I'm sure glad I had two attack spells, dang.
Is Light the only significant debuff in the game? I feel like it's pretty much mandatory past floor 2, since even a single use is generally enough to put Cure's healing/round above the enemy's DPR. I guess Cure is also mandatory, though, past floor 1.
Are items set? I got Luna's Sash of Healing on my victorious run through which was also the first time I didn't go to the boss ASAP and that item is both hugely useful and, if items are set, paired with a ring that seemed hugely not. The shops aren't really very helpful nor expensive in this game, so the extra money would I guess be nice for score maybe but not really contribute to beating the game.
Anyways I had a lot of fun with it and I hope you continue to work on it so I can see the whole story fleshed out and find out what happened to the two Sages.