Absolutely incredible game. It reminds me of (The) Gnorp Apologue, in both art direction and gameplay mechanics. It's an excellent feel. You've absolutely harnessed all the tiny little details to make the game beautiful. The wizard's conversation with the orb is charming, and the way he teleports around the tower with an audible little (pop) is excellent. The animations for the study and the spirits work incredibly well with the art style and give something interesting to look at in the otherwise dull period of grinding that every incremental game has.
As for issues, they're all quite superficial.
I have a particularly large monitor, so the rightmost mountain and background sprites hid themselves before they left the screen. I could also scroll quite a distance to the right of the tower, giving the impression that the space would be used (perhaps for a small village that interacts with the bank), but it never was. The orb ended up quite small in my view after prestiging, as well, as it didn't zoom back in to it.
When the maximum of an upgrade was bought while "hide maxed upgrades" was on, the upgrade's description would remain on the screen until another upgrade was hovered, persisting through movement of the wizard. It could be fixed by showing upgrades, hovering one, and hiding them again, but it seems like an easy fix nonetheless.
As for gameplay, I very much enjoyed it. The different resources interact in lovely ways, and the spells are a good way of giving a method of interactivity after the idle generation of resources far outpaces the manual generation. Prestiging is satisfying, and it's nice that you stack each prestige's progress on top of each other so that you never truly feel that you're wasting time, even with a hasty reset.
For the gripes with the game itself, there's a few, most of which would probably be solved in the process of expanding this prototype to a full game.
The 3rd tower upgrade, which unlocks the prestige feature, is my first complaint. It's significant at first, the herald of a new layer of depth as those upgrades should be, and then in later prestiges you gain... not much, really. It has no functional effect on your existing run. Perhaps adding some effect that only activates from the third upgrade and beyond, like a bonus to magic based on your total accumulated prestige points? Something to make the milestone worth shooting for even when you know your run's going to go to the upgrades past it.
The academy and bank are interesting, and unique in their own ways. However, the bank is a bit inflated to begin with. Large numbers are fun, but it would be nice to start off with tens and twenties rather than skip straight to 500. The lack of any initial use for the bank until you accumulate 2k coins is also a little sad, especially when you then have to shut off production of knowledge or magic to speed it up to get the academy.
Of the sliders and spells, they're neat ways to allow you to focus the resources you need. However, they become a bit of a chore to manage, a problem I bet will be exacerbated by later content. Some control center that allows you to manage those sliders from one place, perhaps connected to the spells wing, would probably ease that burden in a later tower upgrade. I did like how the final upgrade allowed for the creation of multiple buildings; it's a good way to feel like progress is ramping up rather than slowing down.
One issue I had with the spell (and slider) system is that there's no incentive to do anything but crank them to the max for whatever resource you want in the moment. It's simply more optimal to specialize in one resource than diversify due to how the multiplicative bonuses work. In effect, that meant that more spell slots were just a multiplier on spell power.
I hope that in the full version, there will be spells that have more complex and strategic functions, like perhaps increasing other spells' power or having a max number of any given spell.
The bank and academy also seem a little bit barren. I think the bank could do with the ability to see inside, revealing a few little goblins or perhaps a dragon wearing spectacles. Or perhaps both!
The academy similarly is still at the moment, but it's also very basic in its function. It's a simple toggle from knowledge to magic, albeit a flavorful one. A mechanic that rewards in some way not minmaxing, like giving a boost to gold or a different resource when the slider is at its center (after an upgrade) or allowing you to train apprentices that act as an alternative source of magic would add more depth of content to those areas.
It would be nice for upgrades to the tower to affect some of the previously created buildings, like adding new upgrades and the like. Locking the Gold spell behind the tower upgrade that unlocks the bank is a little quality of life change that can prevent unnecessary wastes of resources.
All in all, an incredibly charming game, worth playing through even in its basic state.