Procedurally/randomly generated content
User definable content
There is NOTHING wrong with not requiring 70 hours to "complete". In fact, a lot of casual games offer gameplay that NEVER completes. There is no end. You simply play the game, like a hand of cards.
Randomness (like shuffling a deck) can add a huge order of complexity to the variations a game can have. I would highly recommend it as a starting point for any game which wants to involve players for a long time.
That doesnt mean huge completion times or long play sessions. It just means that if you want to make a game that is replayable, then make good rules and procedurally generate the game-state initially.