It seems to me that goals can be a big benefit to player stickiness. This is actually proven in the level grind design as player's have the prime goal of advancement. Gear based on level and gear sets too.
Collectibles, in their many forms, are another goal that many players like.
I'm leaving this open for any sort of comments about in-game goals. I think the more then better for any game. So lets have it. What kind of goals do you enjoy, what is missing or rarely seen, and opinions on the topic.