I'm neither a 100%er or an achievement addict, a good portion of my favorite games don't even have "Cheevos", which I guess comes from the PC being my platform of choice despite the consoles I own.
That said, I think that there is actually a certain rush involved in finishing a game to your satisfaction, irregardless of what that level of satisfaction is. It's sort of like building a really complicated puzzle, a lot of the joy comes from succeeding and realizing you figured out how to put all those pieces together, not so much from the actual journey to get there. You realize a lot of people wouldn't have the patience to do that assuming nothing else is involved.
The thing to consider is that these "completion" games are very popular, they keep producing more of them. Obvously, no matter how it looks, people are getting some enjoyment out of them. Even if you want to start talking about addiction, there has to be something there that is appealing to begin with for there to be a psychological addiction. Unless of course we learn at some point that there was some kind of unknown hypno-mind control component to thse games we never realized of course...
I think in the end, you can see gaming as being a lot like sex. Someone who has a fetish that you aren't wired for, is going to be beyond your understanding since it all comes down to instict and feeling. Watching someone who is into fecaphillia, water sports, hardcore S&M, or whatever else might even disgust and apall you as an outside observer. Especially if the actual satisfaction actually comes after the actual acts themselves which can be hard for some to understand.
Not a perfect analogy, but the point is that if collection games aren't your "thing" your not really going to get it. What's more like a lot of things that appeal to people, it can be hard to explain exactly WHY they are into something, especially when they aren't having fun doing it for long periods of time. It's typically a matter of working towards a specific high that is seen as being worth the efort, and really can't be explained to a non enthusiast.
It's sort of like how I'm into serious RPGs, stats, and turn based combat. People who aren't, don't get the appeal. You either get some things, or you don't.
Truthfully I *DO* think there are disruptive games that exploit people and are a detriment to the industry, the players, and future development despite the truck loads of money they make and their popularity. That judgement has little to do with whether I like them or not.
Speaking for myself I will also say that as a stat obssessed turn-based RPG player, Pokemon has had little appeal to me despite on the surface seeming to be made specifically for people LIKE me. Largely because the elements built around those mechanics aren't appealing to me. Pokemon is too cutesy, and seems like what should be a side activity in a bigger game, rather than the focus for an entire game itself. I look at the old action-RPG "Lost Galaxy" (I think it was called) where you had a bug hunting and collection mini-game, where you found the bugs on differant planets and could enter them in competitive tournaments for rewards. Sort of like preying mantis or cricket fights I guess. Pokemon is like if they made that game even more cutesy and childish and removed everything else from the game except for that side activity. It just can't hold my attention for long.
Given the relatively small size of Pokemon games, and the simple fact that they seem like they are relatively cheap to develop, I think someone who actually realizes that they could tape something like this into a bigger RPG game (with rewards as Yahtzee points out) with this level of depth would be onto something, as it would greatly extend the play life of the game in question and add to it's overall depth.
