Disclosure: I have been a customer of SE since 2003 ( post split into 3 due to character limitation)

Things to consider about an MMO, its player base, and the playability of the game / Enjoyment.

1) Social Aspect : Multiple things players can do with ease together with minimal wait time. Grade: B+

2) Challenging content: Instances/Dungeons, Raids, Variety of Paths of progressive content that it takes time and skill to reach the goal and cannot be done in a solo fashion. B- (Gating content merely to make it last longer between updates as opposed to developing enriched and fast paced adventure growth with the vast subscription base leans more to greed than limitations so that gives the B-)

3) Personal Growth: Solo content that a player can relax and enjoy in a flexible manner in their own time constraints as much or as little as they so chose. A+