In an age where everybody defends "his" MMORPG with religious fervor, I am still an agnostic. That is to say I don't believe there is any perfect MMORPG, and see good and bad sides in each of them. Of course by saying "game X has both good and bad sides", I'm getting labeled as a game X hater by the game X fans, and as a game X fanboi by the game X haters, but that is inevitable. Also inevitable is that any game has its ups and downs, and by just reporting on the state of a game objectively, the positive and negative comments flow with the peaks and valleys the game itself goes through.
Case in point is World of Warcraft. WoW right now is at one of its peaks, with this weeks patch adding the final piece of the puzzle to the Wrath of the Lich King expansion. Thus finally WotLK has what I would consider a good amount of different raid content. And in parallel the dungeon finder revived or kept alive the 5-man dungeon content. So there is a lot to do right now in WoW, and in consequence the game is highly popular, with people resubscribing, and servers being relatively full.
But once you are on a peak, the only way is down. I agree with the general assessment of Game by Night Chris that World of Warcraft is heading towards a valley of people getting burned out and bored, cancelling their accounts, and a generally diminished interest in WoW.
On the 5-man content side, the problem is simply that there is only a finite number of dungeons to run through. Speed runs through content for which you are already overgeared are relatively boring, and if you do several of those every night, sooner or later you can't stand them any more. Once you have all the possible gear you can buy for emblems of triumph, only the two emblems of frost per day still provide any reward. Some people are already at this point, and over the coming months many more will arrive there, so the interest in heroics will decline sharply.
On the raid side things look similar. My guild isn't the world's most advanced raiding guild, but even our raid calendar looks like this: ICC, ICC, Onyxia, ICC, ICC. Naxxramas and Ulduar are practically dead, and ToC is run with pickup raids. In a few weeks all the raiders will have killed Arthas, while all the non-raiders in their emblem gear will notice that they can't get a spot in a raid. Blizzard could fix part of the problem with introducing a cross-server Raid Finder, but as that would require them to rethink the raid lockout function that isn't all that likely.
So the most likely thing to happen is that soon most players will either have "finished" Wrath of the Lich King, or they are standing there in full epic T9 gear with nowhere to go. Given Blizzard's habitual development speed, patch 4.0 and Cataclysm are still over half a year away. Even the release date of Cataclysm probably won't be announced before Blizzcon in August. Thus this summer will most likely find World of Warcraft in a much worse state than now, with subscription and activity numbers dipping, and bloggers either writing about other games or ranting about boring WoW has become. Of course everybody will be back for Cataclysm, but you can't keep a current game alive all that long just with the hype over the next expansion. World of Warcraft is heading into a valley, a down phase, in the summer, there is no doubt about it.