It's surprisingly not too bad
The concept is solid, the idea is not too original but it works great, graphics are decent and it's always a pleasure to slaughter stuff mindlessy.
But this submissions has some leaks and needs some ideas and improvemente, for example:
Better animation: They're not too bad, but still they're too robotic and repetitive. It would be great to have different animations on enemies and you attacks.
More classes: Only one is way too reductive: you need at least other three.
A story: I like the concept of meaningless slaughter of skeletons, but perhaps a generic storyboard would improve the general atmosphere.
More items: I felt really disapponted when I found out there were no more items to buy and to equip, you need to implement tons of them: people loves that.
Less generic enemies: I know, skeletons are evil and wrongdoers but some variations would be much better. Also, bosses.
Better controls: They're stiff as fuck, that leads to the animation point since you can't attack or jump if the animation isn't complete.
Landscapes: Seriously, one is never enough. Same for music.
Where are the sound effects?
Level up: I noticed it by chance, a more visible benefit from level up would be great, addng a bar that makes you notice that would be even better.
Why can't I attack while I jump?
Implement that and the game may be actually cool, but as it is is rather limited and redundant.
I'll give you a 6 because it needs improvement, and a 3 because I enjoyed it for a good quarter hour.