The game is mildly entertaining leveling 1-90.
Still not very fun while gearing up (unless the xpac is fresh)
After a lot of effort leveling, and gearing up (Weeks or months of work) the game suddenly turns from meh to the most entertaining thing I can imagine.
Progression raiding, high-level pvp, and all the stuff you can do in your downtime makes for one game that is WELL worth the money and time investment.