I've been somewhat intrigued by the "traditional game with a twist" genre ever since I heard the "Sudoku... with a gun" joke in a Mechagamezilla video. I don't like solitaire all that much, but if you can also beat up a dwarf at the same time that seems like a worthwhile experience to me. Besides that, the game is highly accessible because everyone has played some variant of solitaire at some point.
I think the core gameplay is solid as it is. I'm fine with RNG because it's a card game and that's unavoidable, although some classes are definitely more powerful than others. Particularly, the Samurai gets a free draw which essentially makes its skill worth 3-4 MP as opposed to the regular 5 and possibly enables further plays.
Any skill that mitigates the effects of luck is going to be really powerful. Also, playing luck based games with other people is always more entertaining than playing them alone because half of the fun is watching the other player react to their misfortune, something which a bot can't easily replicate.