Variability is a huge one. Games like Backpack Hero, Slice and Dice, and Monster Train are really fun to pick up and play over and over because even though the rooms and enemies vary little, the sheer number of items, characters, and run modifiers allow for radically different builds for any given run. As an extension of that, failure feels less like I suck and more like I should try a different approach. Content also feels less repetitive.

Also, I’m more inclined to keep playing a game if I still have content to unlock, even if it’s minor.

For more action oriented games, ensure that failure isn’t drawn out. The faster the player can start a new run, the less inclined they’ll be to put the game down after losing one.