Good game
There are two downsides to this game.
The skills are rather boring, they do not really do anything that special or strategically clever. it's mostly just a damage spell or a stun spell. Preferably there would be spells that have synergy. So that you can chain spells together for a good effect. For example you could have a spike that throws enemies up into the air, and then have a fireball that can hit them in the air. So you can chain your spells.
The enemies also need more variety. It's mostly: Melee, ranged, medium ranged melee, and king. Just with different textures. It would be nice to see a world that is not perfectly horizontal. Maybe have some archers hiding behind a fortification, or just a hill so that you can stay on top of the hill to counter archers, and rain a hell of fireballs from up top.
Just some ideas. I like this game, it is solid. But consider those options for a future version. I approve of the donation system, although to quell the mass amount of complaining you could offer an option to buy those special items for an increased price of in game currency. Something expensive, but still do-able. Then people wouldnt have the option to bitch about it
Potentially allow easier map movement between areas you have already beaten. (Rather than moving one square at a time, the option to click somewhere else and have it move the squares required for you)