How do you measure whether the MMO game is a successful one?

We can easily judge the success of traditional MMO game before as: game companies will basically accord to subscriptions to measure the performance of the game, and users can then determine whether it is a successful game. In addition, online users at the same time (note: the number of players within a certain time online) is also quite important, but the data it is not open to user, that main because of active subscriptions, compared to the data is easier to expose the negative situation of the game. And a successful MMO will also promote the gold, items and power leveling in game, such as the Guild Wars 2 gold has also done much help for the uses and has made a big contribution to the game company.
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