Doug Creutz, financial analyst with Cowen and Company, made headlines this week by calling SWTOR "highly derivative of World of Warcraft", and suggesting it probably wouldn't ship this year because it wasn't ready. The latter part tells you how little he knows: MMORPG's release date is independent of their state of readiness. My criticism of the former part is more subtle: I do think that SWTOR is highly derivative of WoW, but I don't think that it is that which might cause this game to flop. Rather I think that SWTOR will flop if it turns out to be not a well enough done highly derivate game.
For all it's failures, Cataclysm upped the ante on the new player experience of quest-based gameplay. My wife, who is still playing WoW, and is leveling a new paladin, called me over several times this weekend to show me yet another cool thing she discovered: From boats to being accompanied by a dozen mini-manticores, World of Warcraft now has a lot of quests which go way beyond the simple kill ten foozles quests of yore. If SWTOR would be highly derivative of the latest level of execution and polish of World of Warcraft, I think they would do quite well. If SWTOR is highly derivative of the WoW of 2004, just with voice-overs, it is far more likely to fail.
The main problem for SWTOR however is that its bar for success is so high. I would say that RIFT is doing quite well (in spite of being much more highly derivative of WoW than SWTOR will be, due to playing in the same genre), but if SWTOR only arrives at the same level of success as Rift, people will consider SWTOR a failure.
I don't know how many subscribers Rift has now. Trion is making misleading statements about being close to selling 1 million copies of the game. For comparison: WAR sold 1.5 million copies on pre-order. A million copies sold is not the same as a million subscribers. Given the number of subscribers, churn, and over 6 years of placing high in PC sales charts, I would estimate that World of Warcraft by now has sold over 50 million copies. And that is just the base game, not the expansions.
Anecdotal evidence suggests that Rift is doing well, but not quite as spectacularly as the initial hype suggested. Bloggers like syncaine pulled a Keen and now post mostly critical things about Rift, or have just silently dropped the game. My best guess is that Rift has between 300k and 500k subscribers, which is most probably a financial success, given the estimated 50 million development cost. But as SWTOR's development costs are rumored to have been 300 million, this level of success won't cut it for EA Bioware.