Alot of the reasons I'm quitting were mentioned already.
About this game feeling like work... It depends. I have a very warped view being a Bard and I can view the entire game as monotonous work because Bards ALWAYS follow a preset chain of actions which almost NEVER vary. (Etude myself -> Madrigal -> (Prelude?) -> Elegy -> Requiem -> Minuet -> Ballad II -> Ballad -> Threnody & Melee if the mob's not dead by then). Other jobs though are alot more fun.
And the game IS monotonous and work when you get to the higher levels of just about any other job. Having to spend a week or two straight farming to get a ludicrously overpriced item that's viewed as REQUIRED is NOT fun and HORRIBLE game design. Every method Enix put in of making gil in this game is absolutely long, godawful, and implemented horribly. As a Bard I didn't have to put up with that much (we only have two expensive spells and it's in the range of 80k each, which is the low end of something considered "expensive"), but it's still a major factor for my quitting.
I felt the compulsive need to switch to WoW after I played the stress test, just because it's done much better. In FFXI, you're required to put in at minumum 4-6 hours straight to make any progress. WoW you can log in, play for 30 minutes, SOLO, and make SOME sort of progress (be it experience-wise or money-wise). Enix not putting any solo activities in this game was a BIG mistake.
Still, if you have the time to put into it, it's a fun game, and I'll miss it. Every time an FFXI song pops up in iTunes, I have the incredible urge to jump back in and play it again, but these few (but major) oversights stop me.
Edit: Just so you don't misinterpret this post, I have an equal number, if not more, good things to say in this game. Anyone who knows me enough from the Linkshell though knows it's not in my nature to praise and I bitch a *lot*
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