There is a common theme at the moment, why I play World of Warcraft, and the answer I have is really that I don't know, in many ways I enjoy the game a lot, the atmosphere and the camaraderie, the banter on Ventrillo and yes the achievement of killing bosses. In short its really fun to simply play with other people and to have fun doing something that takes some effort and forces you to work together.
Last Wednesday we Pugged Gruul's Lair and Magtheridon's Lair, well when I say pugged I mean 18 or so from our guild, 5 or so from the 2nd best raiding guild on the server and 2 friends from similar guilds, we one shotted both bosses and it was too easy, but the fun was there, we pulled together, joked, laughed and had fun. Clearing the instances wasn't a challenge for the group we had, but some people got gear, others got some nice pvp tokens and it was a fun thing to do, after all Raiders like to Raid.
So since I do enjoy content we outgear for the fun, its odd that Zul'aman was more fun on my Warlock (we dinged 3 chests having 2 wipes on the Dragonhawk and a generally slow start), than I did on my Paladin (7th bear in 7 resets). Its not that the Bear runs aren't fun, we don't take them too seriously, we hit one with 6 minutes to spare and 2 wipes and 2 trash pulls we didn't need to do. With my Warlock however we were pushed, we could possibly have gotten the 4th timer if we really really pushed, but it didn't pull together, but it was fun. So what is it that makes it more fun, I suppose really its the challenge, the group my Paladin runs with hasn't been pushed by it, our lowest dps hits > 1k dps sustained, and our highest can hit 1.6k sustained, simply we reached the stage where the timers no longer offer a major challenge because of the raw DPS, its like Gruul and Magtheridon, we could 2 healer the fights if we needed to because of gear, so the risk and challenge is reduced. My Warlock's group by contrast, we had two dps over 1k (me sustaining roughly 1.16k dps, and a shaman at 1.2k dps, the rest hovered in the 0.7-1.1k dps range, with similar damage to myself and the shaman due to differences in activity).
I love the challenge of the game, and I think a lot of other people do, pulling 14 mobs in Heroic Shattered halls is the kind of thing thats fun because its still a challenge, getting it up past 15 is the next challenge, and I hope WoTLK brings that, a way to really challenge yourself in an instance like ZA irrespective of your gear level, because that would be interesting, something you can always run when you need a challenge, something to make you come together as a team.