I've heard someone compare the collecting in video games to hoarding, a type of obsessive-compulsive disorder, but I believe those two have one significant difference; the goal. Hoarding or just basic collecting rarely has a clear ending point, whereas video games can't help but have their limits and so the player is always capable of "catching em all". Collectors are more like perfectionists, looking for that absolute completion that real life can't offer.
That is why designers should always award the player for getting that glorius 100%. Even if you can't offer actual rewards, like an extra map or infinite ammo, simply acknowledging the player's hard work with a golden star or a few words is plenty enough.
I received Super Paper Mario for Wii this Christmas, and after 60 hours of playing I was finally done with all the cards and recipes and treasure maps. And the game said nothing. Of course the completion was still satisfying, but the anti-climatic ending left a part of me disappointed and feeling like I wasn't truly done yet.
Being able to see how far you have gotten also motivates and engages the player like nothing else, be it the amount of collectible items or a percentage of your overall process. I've found myself playing games I'm not too fond of for countless hours simply because 68.7% just doesn't feel like a good place to stop at.
That is also why role-playing games are the most addictive of them all - seeing your characters grow and get stroner little by little makes us all resort to the "just one more level" excuse more than once.
- TM
