A lot of playthroughs isn't called a challenge, it just means you have to take longer to finish the game. Even someone with relatively low skill could eventually win by accumulating enough starting money. A real challenge is when you don't get any bonuses at the beginning of the game for having played before, and you must play through the entire game to win. That game would be made hard, but not unbeatable. Multiple playthroughs would only happen because the game is hard, not because the game requires them to win. So instead of grinding for money, you'd be grinding for actual skill. Two games that take an approach like this are Nethack and Touhou, and both are great games.
That said, this isn't a bad game, you just can't call it "challenging".