If I had a penny for every time I read the words "WoW killer", I'd have enough money to buy all of Activision and create World of Warcraft II.
Also, SWTOR is a great game but have some VERY serious issues:
A) the game had way too many bugs in it and still does -- it's basically a "paid beta"
B) the lack of grinding makes getting to the maximum level quick and easy
C) end game content -- the problem is that people reach end game content quickly because of reason B. Furthermore, there isn't much time to develop end game content as a result. People get bored easily and quickly with a game built like that.
How do you solve these issues? Tone down the "easy" difficulty of the game. Make the game require more grinding, but not necessarily at vanilla-WoW levels. When it takes longer for players to accomplish in-game goals, it gives the developers time to come up with more end game content. That way, when the players hit max level and grind all they need, there is plenty to do in-game to keep them satisfied.
And let's not forget the most important solution: patch bugs immediately! Don't wait 2 months and fix 150 bugs all at once! Patch them quickly and in small patches if need be! Bugs make players angry and frustrated. Remember that a frustrated and angry player is more likely to cancel their subscription!