I have watched your video and enjoyed it, it was very useful as it showed me a lot of things that could be improved or made clearer to the player.  It is unfortunate that you were unable to finish it but this is understandable as there were many things (like the magic feature) that I now realize were not sufficiently explained to the player.

While watching I took some notes about different parts where you had been confused and would like to clarify some of them, I've also included time stamps so you can see what I am referring to.

Time In Video, 3:37 - For some reason the tutorial text boxes were not displaying correctly for you, there should have been a box behind the text to make it easier to read.

Here's how it looked for you:

Here's How it should have looked

I am not sure why it displayed incorrectly, and I will try to fix it for future versions.

Time Stamp, 6:46 - To clarify, the reason for why touching enemies hurts you is to make sure you can't run past them when you shouldn't, at least, not without getting hit

Time Stamp, 10:00 - I agree, you should not be booted to the menu after dying, I will fix this in the future, thanks for the suggestion.

Time Stamp, 12:16  - This is a health orb, it heals you when you hit it (but you had max health), the tutorial mentions this but sadly due to the bug mentioned earlier you may not have been able to read this (I may have also forgot to include that tutorial, I will check)

Time Stamp. 12:36 - You can change the size of text under Options -> Accessibility -> Text Size. Making it bigger may help you to read the item descriptions and the name of items when you pick them up

Time Stamp. 36:00 - I think the hitboxes may be broken here, you should have been able to hit this enemy easier with the lance, I will fix this for the next version

Most Importantly:

To use magic you have to hold the spell toggle button (By default W) and press the attack button (By Default E), you can cast the spells as many times as you like so long as you have enough mana (The blue bar at the top)

Another thing I realized is that the second half of the demo (where it goes dark) is not easy to understand at first. A big part of why you had difficulty with that second boss is because there were new weapons and spells in the dark version of the level (Two weapons in the tower area, and a spell where you first unlocked the dash ability), I can see why it would not be clear that you should explore this area fully, sorry for not making it more clear. If you ever decide to revisit the demo hopefully with this new information you would be able to complete it. 

Thank you for checking it out though, your feedback is helpful, I've had two other people test out the game but they've been playing it since the first demo, so its useful to see someone who had never played that demo try this new one, so thanks for your time.

Whether or not you decide to go back to the demo, I hope to speak with you again in the future, and I will inform you whenever I make any new releases or major updates. Again thanks for your time.