I'm seriously starting to think that the leveling experience in most MMOs is pretty much useless. Back in the day (and some still exist) there has been games where leveling has been near never ending and the system revolved around your characters level (or power). Now, with most mainstream MMOs being casualized to the point of having the leveling phase last for just a few days played, whats the point? Can't we have a story line and quests without it being a means to gain levels? I for one can't enjoy the leveling of WoW or most other games because I'm already spoiled to what the endgame might be. And the endgame just tends to be so much more interesting that the leveling phase is just a drag and something to get done with quick.
However when I do quests at max level it is whole different story. I can actually get immersed and take my time with the stuff.
Thus, I believe the next awesome mainstream MMO(RPG) shouldn't have actual levels at all. I believe a system similar to Guild Wars (the first one) where you gain skills by doing things would be pretty decent to start off. Gearing is one thing, but I believe wide array of customizeability and how your character would work is way better than straight off power upgrades (item levels in wow).