Not bad for your first time.
Although, let's admit it, you totally ripped off Castlevania's castle entrance (from SOTN, AOS, HOD) with the most parts of your castle level. But the tiles are certainly drawn by you, you have my respect for that.
Now, let's get to the bad parts:
1.Enemies: That endless spam is waaay too cheap. Give them real AI, make them wander the room and/or follow the player, give them attacks.
2.Speaking of attacks - add a few for the player. That one swing is just booooooring. Make combos, different attacks, etc. But, I must commend ya, you have made an attack for each position, that means you do know what you are doing.
3.Boss. Let's be honest: Dumb, Bland'n'Boring. He lacks any real AI, although he does have some semblance of one. Give him cool attacks, make him more threatining to a player, make him at least somewhat smart!
4.Story - overdone way too many times already. It needs progression, twists. Or you just need to stop beating the dead horse of "we are the bad guy" story. It's your choise, really.
Summary:
Make some real battle system, for both Player and enemies!
Make some more story!
Make more gameplay mechanics and variety! Whether that would be enemies, stages, stage hazards, or just visuals!
Have a good day man, you've earned it.