In the case of LBP2, the urge to collect everything is just as frustrating and time-wasting as any other game, but the reason I feel utterly compelled to catch them all is because the feature that really makes the game special -- editing your own content -- is technically incomplete until everything has been collected. Instead of stars or bananas, materials, songs, stickers, and costumes -- all important to editing -- are hidden, and the urge to collect becomes irresistible (and not necessarily amusingly so).
The case of Batman was a polar opposite because I was looking for any excuse I could think of to play the game longer. I really felt like I was gaining not just a mastery over my grasp of the world around me, but my expertise at combat in particular, going through several of its challenges. The more I played the better I got at getting through combat with high scores and enormous combo chains, and that was true from the beginning of the game all the way to the end -- an impressive feat for such a simple combat structure -- though I understand some friends didn't get the same enjoyment out of it.
Exceptions to the rule are interesting.