Cultist Simulator is charming, and yet it gets under your skin in a very uncomfortable fashion. It breeds obsession, even madness, then eventually boredom.
It has a good progression and that it eventually outstays its welcome does not make it a bad game. It's certainly inspirational. It's just that the card based system eventually lays bare the game engine. So raw and exposed the temptation to exploit it becomes overwhelming. Why not repeat the same actions over and over until you have effectively infinite funds? It gives you a stronger board position for the next stage of the game. Boredom is something humans create, not an independent entity. It is valid to say that the players are the problem, it is equally valid to say the designers are at fault for making mechanics that function best when repeated over and over.
Cultist Simulator could have been a great game, as it is, it has the trappings of a great game, with the mechanics of an unfinished one. This might seem unfair but that is the nature of existence.