It entertained me for a while, but I didn't dive too deep. I reached level 9 without much effort. The time I played, I noticed a simple but original idea. I haven't played enough to determine if there's more hidden, but I haven't really felt like doing so either.
I seriously doubt that this game was made in just 10 days, and in any case, it's very suspicious that its resemblance to the theme is the same as any other random game. Designing a card game can't be done in just 10 days. I don’t think the creator of Slay the Spire made the game in only 10 days. It's true that the idea could have been conceived before the jam legitimately, but in any case, the execution is complex, and it has three difficulty levels—I really doubt it.