Really fun game, played it to completion! It played a bit more like a regular platformer than a metroidvania though, but I still enjoyed it.
There are a few places that I think could do with some more polish - for example the music really needs to be a bit longer or maybe there be different tracks for the different areas... at the moment it can be a bit repetitive! Also, once you have the longest sword it's possible to damage enemies through the floor by jumping up underneath them. Also, the boss can be cheesed a bit by just standing really close to him and spamming attack... In fact, most enemies are not that challenging apart from the floating purple guys who are dangerous!!
A couple of other personal preferences; the jump is a bit floaty, especially when you get the higher jump... also I think that if you add in a bit of coyote time it would improve the feel of the early game when you are trying to jump off the staircases etc. Its less of an issue once you have the double-jump as you can still jump when falling from the platforms.
Overall though, great game! Well done!