I've only ever gotten 100% on two games in my life: Batman: Arkham Asylum and Super Mario 64. The first one was because I absolutely love riddles and puzzles, and even though very few of them were actually "riddles" it was very enjoyable to explore and find the solutions to them. That one I did without the help of gamefaqs, and it took me a few months of 1-2 hour spurts in the game to finish. Super Mario 64 I did because I had a strategy guide and thought you could ride Yoshi when you finished. I was so disappointed.
I bring this up because I'd like to talk about Achievements. Pretty much every 360 game ships with them, and a good 75% of them are given just for playing through the game. The other 25% are collect X number of doodads within the game. In World of Warcraft, this follows a similar pattern. You gain achievements for just playing the game (Boss kills, dungeon completes, level 20/30/40) and you have your collecting doodads (Loremaster, Lots of Pets, That Mount One I Can't Remember Off The Top of My Head) and then your miscellaneous ones.
So, why on earth do I have 100% in Arkham Asylum and not Loremaster?
To give you an answer that doesn't involve being the goddamn Batman, I believe it has to do with two factors. The challenge of the achievement, and how interesting that challenge was. You see, the best thing for me wasn't showing everyone online that I beat the game, it was simply that I enjoyed the challenge.
Loremaster is by no means an easy achievement; neither is Insanity, or Lots of Pets. However, the difference is that the challenge doesn't come from completing the actual achievement, it comes from the fact that it takes a large amount of time and travel. That, and actually beating down the quest mobs, but if you're doing this you're probably level 85 anyway. In Arkham, (assuming you weren't cheating) you were directed to the area it was in, but left to figure out the rest via clues in your notebook.
What I am suggesting here is not that every game should be like Batman, as tempting as that might be. I believe achievements should be challenging, interesting and rewarding. Not in the sense that it gives you something tangible at the end, but that you feel like you actually accomplished something cool. I don't mean to say that those who have pursued those achievements don't deserve a pat on the back. I'm just looking for something more engaging than doing the same thing I do in the game anyway, just in a different locale.