I'm looking forward to playing more, but at the time feel that the content is too linear. I don't want to plow to level cap and then move up the instance ladders which, while certainly fine for launch, doesn't much appeal to me.
Once subsequent patches flesh out (and introduce) some of the other activities -- such as crafting and gathering, and hopefully a support class -- and add some more lateral content, I plan to be there at an unhealthily obsessed level. I'd also like to set some kind of insanely long-term goal (that isn't something as arbitrary as "get everything to fifty") and chip away at it for a year or two.
Here's hoping I have cause to see you chaps (read: argue and be generally snarky with you chaps) for a while to come!
Although I'm planning on sticking around and running dungeons at endgame (a first for me), I agree and hope that there is more horizontal content. Honestly there's a lot there already within the various "logs" but I'd like to see real NMs, sidegames, player created dungeons (a la Moblin Maze Mongers) and just side quests until the/(an) expansion comes out.
However I do think Yoshi has thought about all of this and I think for the most part a lot of this will be addressed.
I'm still waiting for Ishgard, a THF and NIN class, housing, and whatever else is in store. And if and when the expansion comes I'm hoping for an 8 or 24 man LB quest to continue leveling. It doesn't have to be that hard, but since most people will be at 50 and the DF should be optimized, things like these should be a lot easier logistically than they were in FFXI. And that was more than half the battle.