Balatro

Poker hands plus jokers. The rule set fits on one page, but the combinations that emerge as jokers feed each other get completely out of hand.

That is the definition of good system design: few rules, many outcomes. Getting complexity from the interaction rather than the count.

It was made by one person, under a pseudonym, with no marketing budget, and it sold millions — exactly the case I look for in Radar, except it is far too well known to qualify.