Equal all-time — according to https://www.dekudeals.com/items/slay-the-spire. It seems to go on sale every few months.
Bought it recently on a mate's recommendation; you lose track of time when playing. It's addictive (and hard so far).
Metacritic score 85, Opencritic score 89. Considered one of the best deck-building games out there.
Note: Slay the Spire 2 is scheduled to be released on PC soon. So keep that in mind in terms of possible buyer's regret.
No need to wait for 2, it will probably be EA anyway, and they dont even have a release date yet.
You can spent a good 200+ hours on this while waiting