I came back 2 weeks ago for Warlords of Draenor, hadn't played since ICC was released, and used my 90 boost to go straight to endgame.
I must say, WoW is a much more fun game, at least for me, compared to WotLK days.
First of all, the options at endgame are much greater compared to WotLK, and are much better polished and refined than they used to be:
Raiding - Inaccessible to me for the most part in WotLK, but since I discovered LFR in the game now this whole swathe of content that I'd only dip into once every now and then has become an integral part of my endgame experience. It's easy to be sucked into LFR because of how convenient and fun it is to zerg around with 24 others and raid for loot, scenery and fun in a casual environment.
Levelling Polish - I left before Cataclysm, so I have a vast amount of content to experience in this aspect
and, come WoD,
Garrisons - Very welcome addition in my opinion
I used to hate the dailies in LK, but I actually find that I enjoy doing these "grindy" activities nowadays, I'm simultaneously levelling one character of each class to experience the content, on both faction, consuming endgame content on my 90-boosted main character, levelling my professions, gathering pets and mounts, maximizing profession skills and so on.
The responses you've gotten thus far in the thread appear to be from those who are burned out and jaded, or have played continuously for a long stretch of time and so activities like reputation maximizing, dungeoneering, achievement hunting, levelling, dailies; everything's become a grind.
Depending on how long you've been retired, I'd say you'd be surprised how much fun can be gotten from WoW nowadays compared to the earlier X-Packs, where you were restricted to sitting on your mount in the capital and shouting in chat for PUGs for hours on end. Now, I'm on my character out doing stuff in the world whilst being queue'd for LFR/LFD/PvP and enjoying the game to its fullest, taking my time and avoiding social committments to prevent it from becoming a second job with schedules.