Only issue with Rift as far as I can tell is the way they chose to do leveling is a grind. The WoW formula for leveling was roughly 2 levels for every 8 hours of time invested and they held it there since BC.
The Rift formula for SL seems to be 1 level for every 10+ hours of time invested. The grind is pretty brutal right now. My only assumption is people in top guilds formed raids and zerged the ever loving shit out of high spawn point mob locations until their eyes bled.
If you are leveling through IA's and Hunt Rift your xp bar is hardly moving.