Ah, yeah, I can see how that's not readily apparent right away.

There is tension & decision-space among the players. After all, if no-one takes any treasures, you could go all the way to the bottom and grab what you wanted. But as soon as people start looting, they start gasping and using up the tragically-common air supply. Some might deliberately try to drown each other by tactically picking up and dropping stuff. So it's a reverse chicken race, it's a game theory tense wonderful nightmare. All wrapped up in a super-classical roll-and-move shell that's easy to play and teach.

(I was gonna recommend Deep Sea Adventures in this thread! But I see several people are already recommending it, and that's awesome!)

It's not a very strategic game, but from my understanding that's not what op is looking for. It's a very light push your luck game, you want to go as deep as possible to fetch the treasure but if you go too deep and someone goes back you might run out of air. I like it because it's so easy to teach and there's tension to find out if you're going to make it out alive and if it was worth the risk.

Common rule mistakes are playing a single round (I believe the game is 3 rounds) and placing the treasures back after the end of the round. In the 2nd and 3rd runs the path is shorter because it lacks all the treasure you Already collected so you should be able to get the deeper treasures in the later rounds.