Liked the art style, the gameplay, and the amount of mobs/upgrades. However, the game itself is seriously lacking either playtesting or normal game design. Let me be more specific...
1. Game is obscenely easy. I've never upgraded health, and had no serious problems because of it. Yeah, I've died a few times, yes, but that was only because I've got too reckless, not because the game is hard or anything. One of the reasons for this is...
2. ...Magic simply wrecks faces. Seriously. I've chosen nothing but magic on levelups, and never had any serious problems with anything - when firebolt becomes spammable, it is usually enough to one/two-hit anything.
3. Bosses are pushovers. Their attacks are extremely easy to avoid, and they die on first-second vulnerability phase. See points 1 and 2, again.
4. Many upgrades are useless. Specifically - +keys upgrade and +potions upgrade. Also, sword upgrades and all these blocking/charging skills are borderline useless, because they are too awkward to use and not even remotely as effective as magic.
5. Earth Summon is the most useless spell. Its damage/speed is extremely low, its vision radius is obscenely short, and it almost never aggroes anything. In other words, it offers nothing to be even remotely useful.
6. Healing spell is too powerful and makes all these potions redundant in 95% of cases.
7. Giving any spells unlimited range, unaffected by line of vision is just like giving the player a "press X to win" button.
8. Monsters are very passive. These snakes seemed to do nothing but ignore me, even up close - probably a bug.
9. The levelups bonuses need some kind of rebalancing or at least some incentive to not put everything into a single stat.