Unless it has great PvE, its market is severely limited no matter how brilliant the design. And lets be honest, the chances of brilliant design are 1 in never.
PvP games are doomed to a cycle of:
1. OMG PvP is so awesome I can't wait to try this next game 500k-1 million+ boxes sold
2. People realize that in PvP you lose 50% of the time, losing sucks
3. Subs die steadily.
4. Expansion announced. People come back OMG PvP is so awesome I remember this one fight I had it was epic!
5. People realize (again) that in PvP you lose 50% of the time. Awesome fights are 1 in 100.
6. Subs die again.
WoW is a unique phenomenon and most importantly A PVE GAME and once people get that through their heads and start setting realistic expectations of success we'll stop seeing the "next big MMO" super-hyped failures that we get every 6-12 months.
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I'll miss you Eka.

Efaiim, 70 tauren shaman, Kilrogg (PvE)
Sevoac, 70 tauren druid, Kilrogg (PvE)
70 mage (PvE), 69 paladin (PvP), 60 warrior (PvP)