I played vs the AI, which should be a lot of fun if you want people to invite their friends to play the game.
Lots of UI questions about tiny details. For example, when I am casting the fireball spell, do I just play that on my side and then it affects the other player? Can I attack both the other player and their creatures?
A little animation for how each turn you get one more mana would be a good touch. Needs a lot of details like that to compete with hearthstone. Just general polish stuff. It is very polished now, but hearthstone is a beast. And they have a massive marketing budget, so the algorithm is going to show their stuff before yours.
Also, there needs to be some kind of tutorial game explaining what a good deck is. When I was building the deck I just randomly picked a bunch of cards without much thought. Maybe pre-built decks or some kind of meta-game where you collect cards and improve your deck while adventuring through an overworld.
Art is nice, the cards looked cool and moved fluidly. Some of the UI elements were a bit bare bones, and again, every detail needs to be just so if you want to take on Blizzard.
I would love to see a fleshed out single player campaign with a narrative or something like the old MTG game by Microprose. In that one, if your deck was powerful enough some of the bad guys ran away from you which was a nice little power fantasy.
I know everyone says "add daily challenges to improve retention" but I'm not so sure just doing them for the sake of doing them is much reward in the abstract sense. I'm not going to come back to this game unless there is a significant single player upgrade, and I don't think that is an unusual reaction to this kind of setup you have.
If you made the cards wacky and weird that might help you find a unique niche rather than go right at the teeth of the bigger games. Like if your cards were fart jokes and other nonsense that might give you a new audience rather than going toe to toe with a 100 pound gorilla.
Anyway, feel free to DM me, or ping me @michaelplzno and I'll look at other iterations down the line!