Popularity/ Financial Success: used by players of WoW to argue that WoW is the "best" MMO. However, this leads to the McDonalds analogy (I stretched that one waaay too far in one of my early posts). It's kind of elitist, but I think it's also a fair point. How many folks reading this really think McDonalds has the best hamburgers that money can buy?
Innovation: used by players of EVE Online, TSW, and Guild Wars 2 to argue that their games are better than all the "WoW-clones" out there. I do see the importance of innovation. Anything that pushes the boundaries of mainstream MMO space is overall a good thing, since it potentially expands the audience. However, if we want to use innovation as our yard stick of what constitutes a "good MMO" then really bizzare MMOs with tiny audiences like A Tale in the Desert, Endless Forest, and Myst Online have to be considered the best MMOs. Arden: the World of William Shakespeare was innovative as hell, and development on it eventually was halted because players didn't find it fun.
Pooled ratings of Professional Critics: used by players of WoW, SWTOR, and LoTRO (among others) to argue that their games are "good" in an objective sense. On the surface this seems like a good argument, since it evokes the opinions of "experts." However, when it comes to it this is just another form of popularity. History is filled with examples of works of art that critics hated or ignored at first but later came to be considered classics.
Further, I don't find Metacritic scores to be a good guide to whether I personally will like a game or not. Wrath of the Lich King got an astounding score of 91, and when I first tried it I didn't even last out the free month that came with it. Diablo III scored an 88 and, at least among the bloggers that I follow, the overall consensus seems to be that it's a popcorn entry into the series with little staying power compared to Diablo II (no offense to Tipa!). Warhammer Online garnered an 86, and we all know how that turned out. Dungeons & Dragons Online scored an abysmal 74, and it's grown to be one of my favorite MMOs. The Secret World did even worse, and I find it to be extremely compelling.
Obviously what ultimately matters is whether a MMO is fun or not. Just as obviously, fun is in the eye of the beholder. What's perhaps harder to accept is that, like fun, suckage is also in the eye of the beholder. Just because you don't like something doesn't mean that it sucks any objective sense. Conversely, just because someone doesn't like an MMO that you like doesn't mean they have brain damage or aren't as perceptive as you. All you can say for certain is that they didn't think it was fun.
Few of us run around screaming at people over whether they enjoy boardgames (love them), tennis (hate it), or hiking (love it). I can list all the reasons I don't like tennis (I bite at it looms large), but I would never be tempted to claim that tennis sucks in some objective sense. Would anyone? Why then do we get so worked up over whether other commentators "get" or "don't get" the MMOs we play? And why do some commentators feel the urge to go out of their way to antagonize fans of games they don't like? In a some ways MMO enthusiasts tend to behave a lot more like religious fanatics then hobbyists. Do coin collectors and knitters have these kinds of debates?
I'm certainly not the first to comment on this phenomenon. But to me this is an issue that keeps rearing it's head. The internet: the great pit where the flamewars are not quenched and the horse dieth not.