Thanks for the feedback! We do have more art for character progression. We just ran out of time for polishing. Currently by selecting the card, you can preview the outcome but looks like that isn't clear so I'll try making it so it shows the preview like a plus then green colored value or minus and red colored value when selecting cards to play.
Thanks for the suggestions about the UI, we will definitely note that. We have been exploring ways to make UI more self-explanatory so your feedback helps!