This is actually a great game. a lot of what i have to say has already been said but what i haven't seen pointed out is how good a demo this is. i cant really break down how exactly this is but you've given the player access to enough stuff and mechanics that not only keeps them engaged, shows them how the game is gonna be played in the future, but Also keep them in the game and playing. that is a hard thing to nail in a demo, kudos to you!
on the gameplay side of things, i did bump into the balance issues that Alex_x90 pointed out, being that some cards and play-styles are just straight up better that others.
in my experience, the shop the player really has to purchase two cards; one being the candle and the other the wanderer. the abilities of the other cards don't really scale up to them at all.
this is very much an issue that is particular to a demo, adding more content and changing the way the player purchases cards will actually solve this issue. I've thought about this for a bit and imo until you have a good amount of cards for the player to mess around with and just more ways to generate massive amounts of light in general, i think this approach you have rn is fine. but in the future demos, when you've added more content in the game, changing the way card purchases are made can resolve this (you can also look into some games like path of achra or Crawl or just slay the spire as just some examples that come into mind).
overall. a very good game and demo. i very much anticipate a full release and more content. good luck on your development journey <3













