In terms of basic movement and appearance it's good. The character moves smoothly and the jump distances feel good, and the background and animation is clean and pretty. A few suggestions:

1. Leave the zoom distance at one setting. Being able to clearly see how you're moving and where you're going is critical for a platformer.
2. For the same reason, place the screen shifts so that they're not mid-jump or right next to a deadly drop or other hazard.
3. Hold down to look down. Hold up to look up is already available, and down is even more important for seeing where you might land.
4. Moderate the repeat damage from spikes. It was very easy to die from a single slip in the corridor of spikes after the "Did I just tempt fate?" sign.
5. Consider having separate buttons for activating chests and jumping. You want to be able to control which you're using when there's an enemy approaching or you're on a small platform with a chest.

I keep 'using' the iron key which blocks me from any progression, I don't understand how you are supposed to unlock the chests?

This looks really solid and promising. Nice style and presentation.
However, the controls are not great.
Since this seems to be a classic platformer that doesn't use the mouse, it needs a control scheme closer to what classic platforms did. Meaning separate hands for action and movement.

Having space to jump makes sense when your right hand is glued to the mouse, because you are using the mouse, for moving the camera or aiming etc. Having all the actions of the game on the left hand while the right hand is sitting is awkward.

WASD for movement, which is a standard by now. But put the actions on separate keys that the right hand can comfortably press. Like J K I L. This is also becoming a standard
(K jump, J Attack) or something like that.

Unless you plan to incorporate mouse aiming where this wouldn't work. Peace

Looking forward to seeing more... currently ends on a high spot left of the black bonfire?
Got the key, opened the chest, now what?

EDIT: Thanks, finished the game... just a couple of small issues. One is jump doesn't work if you're in front of a chest which in a couple of areas isn't helpful, and controls are awkward.
Lovely aesthetic, nice audio, somewhat annoying grunts from the character.