I REALLY struggled to understand this game. Too much is thrown at you at once (7 stats, 5 disciplines of magic, and a spellbook you have to begin purging before you even understand what the spells are or what they do.)
Probably the biggest issue here is that you're given tons of information about your units and their loadouts, but the gameplay itself is idle, making it nearly impossible to actually see the impact of your decisions. What spell did my unit use that nearly one shot an enemy? This makes it impossible to know which builds to lean into and what spells to discard. Clicking on stats to see a description of them doesn't matter if you don't understand what stats contributed to which spells or which spells contributed to which victories.
Plenty of things on-screen are shown but NOT explained. What is a "lonely" spell? Why are some AOE shapes different colors despite only being one tile?
Other game mechanics are also explained very poorly. There are 3-4 different "contexts" I've noticed between fighting, collecting, the rainbow "riddle" mode (I didn't even realize there were riddles to solve until I saw that there's a medal attached to them) and shops. One of the biggest points of confusion is that I'd give one of my characters a rune to level up one of their colors of magic and I'd see the regular level of a DIFFERENT unit go up. At first I thought the runes gave experience as well as a level in that type of magic. Later I realized that collecting all of the runes essentially triggers an "end of battle" sequence where the experience you already gained has now propagated to your characters. This is super counterintuitive and implicitly communicates inaccurate information to the player.
After playing and failing, I still have absolutely no idea what a good strategy is, and my intuition that having certain units specialize in different kinds of magic rather than being generalists is probably useful, yet I have absolutely no data to show on this account.
In order for this game to be even remotely playable, I think having the name of a spell being used appear as it's being used, as well as some kind of damage indicator that gets bigger when dealing bigger damage would be a good first step. As an example, seeing "Splash" next to big damage numbers would confirm to the player that one of the spells they've invested in is paying off, while seeing "Magic Missile" next to small numbers might suggest a player should discard that spell the next time they're forced to.
The music and voices are okay but nothing special. The game sprites are basic but I like the idea of having the units change color according to the type of magic they're strongest in, and the frame by frame animation for the spells themselves looks fantastic.
EDIT: After playing a bit more, I've found that a generally effective strategy (on novice at least) is to minmax for high levels in specific types of magic, then learn the spells with the highest level prerequisites and discard the ones with the lowest prerequisites. Reaching high levels happens pretty quickly, so conserving gold for healing is useful, as well as experience if a character ALMOST has enough experience to level. Runes to level up a unit's magic are nearly useless unless you already know the tech tree (which you aren't allowed to see.)
I mostly put all my units in the front because there didn't seem to be a straightforward rock-paper-scissors hierarchy between the colors, just that opposite colors dealt extra damage to each other (which isn't necessarily good or bad; it just meant fights would either go by quickly or slowly.)
I'm sure on harder difficulties you have to pay attention to the actual skills and perhaps place support units toward the back, but due to issues mentioned above I suspect if I picked a harder difficulty and lost I wouldn't really understand why. The seemingly endless levels (without content changing or even an indicator saying how far I'd gotten) make it really demotivating to try and "finish" the game since I have no idea how close I am.
The end of the game comes suddenly, and without any real content other than random magicians from start to finish (not even a boss) it's kind of frustrating (and anticlimactic) that the game just ends, especially if you were gunning for some of the level mastery medals.