The idea is solid! (Played 2 times - is there an end goal? 10 minutes?)
The sword swing animation is very satisfying but its hitbox does not seem to match.
I would work on readability, everything seems like it's was blending with each other, for exampole spell effects could be more vibrant but still very good use of assets.
For the upgrades screen - since whole game is clicking (spam clicking) it would be cool to give player some room for realisation that it is upgrade time, for example fade in the dark screen and add card reveal animation.
Also for the card animations I think the selected one should get bigger, not smaller :P
Overall I really enjoyed so please take all of it as a feedback for improvements not me being harsh ;)
And would love to see updated version - with click skills!
Great entry!