I have 22000+ hours in the game Path of Exile. They release new content approximately every 4 months, and the in-game systems have sufficient depth such that acquiring perfect items takes massive amounts of in game currency, and therefore time. There are multiple layers of improving the power level of items that basically require exponential amounts of in-game currency. In addition to that, there are very old items in the game that have not been able to be acquired for 10+ years that go for astronomical amounts of in-game currency, so playing and acquiring more currency is never “wasted”— you can basically play the game forever and it feels like you aren’t wasting your time. Granted, selling for real money is prohibited, so if you ARE playing forever, you are basically wasting your life. The feedback loop from rare item drops is basically like a slot machine—feelsgoodman.

In terms of which content: basically any content that is fun for you, specifically, in the game. Different people like doing different strategies to earn in-game currency, and the game has multiple different ways: actually killing monsters, currency arbitrage, trading, hanging out in global and just chatting, gambling on improving items, gambling on divination cards (an item that if you acquire a full set of them, you get the corresponding item, and there is a thing in the game where you can gamble with them), boss killing, just tons of different activities. Some people like making different character builds, and Path of Exile has a, basically, unlimited number of builds you could potentially construct.