I have watched this cycle with every MMORPG I have played so far. The people who scream the most about the game endlessly on the forums are NOT the ones to listen to. The average gameplayer is not qualified to do game design, even though they think they are. Almost every one of those raging complaints I have read is about 1 aspect of a game design and is often far too personal and coming from far too narrow a perspective.
Now there are people that analyze the game, do endless math, and seriously try to quantify problems, and are making a serious effort to make a contribution and they should be considered, but not the final arbiters.
All too often the developers listen to the feedback from the players and make changes that the players claim they want - but in the end it only helps ruin the game. I far prefer a developer who has the balls to listen to the public, then go back to their design and make changes that are consistent with the game's original design - or even not change things because change is not necessarily a good thing. Sometimes a game element is fine the way it is but the player base hasn't taken the time to really look at it.
Even worse is letting the beancounter's dictate design of course. Just because some other game is popular, does not inherently mean that trying to clone it will guarantee the same success.
Dark Age of Camelot - a *fantastic* original design. Probably the best MMORPG ever designed. It had a great mix of PvE/PvP gameplay and appealed to each camp. It had Roleplaying servers - it had PvP Roleplaying servers even and the RP rules were more or less enforced to boot. The first expansion (Shrouded Isles) totally ruined the original culturally based design even while it expanded the PVE side of the game. It could have been better executed and designed. Further expansions and improvements only made things progressively worse. The developers failed to see what the appeal of the original game design was, and thoroughly overengineered it in the name of putting out multiple expansions.
Star Wars Galaxies - the other contender for best MMORPG in my opinion, despite its many flaws (PvP was at best rather mediocre and generally there was more dueling than actual PvP). An amazing Sandbox design that had a very dedicated community. An innovative game with many features and elements not found in any other titles - before or since. WOW was emerging at the same time though, and so the developers felt the need to make the game more like WOW to capture the millions they saw flowing elsewhere. They failed completely in every regard. The first revamp - the "Combat Upgrade" simply ruined a few elements of the game but was succeeded by the New Game Enhancement (NGE) which was shoved down the players throats without any previous warning (well, they announced it was happening 2 weeks before it happened). This took the game from a Sandbox design with 32 mixable professions and great flexibility to a design where there were only 9 possible character specs. If you were a commando, you were absolutely identical to every other commando in the game in every regard. The game lost probably 85% of its playerbase.
City of Heroes/City of Villains - a great game, although weak in PvP, fantastic loyalty from its fans, but they failed to live up to the expectations of the players who wanted the superhero genre. That said it was a great game right up until the beancounters pulled the plug with no explanation, despite a loyal fanbase, and apparently turning a profit.
Warhammer Online - built by the same folks that ruined Dark Age of Camelot, this game attempted to recreate the same intense gameplay but was so thoroughly over-engineered that it lost those people who had enjoyed the original title so immensely. They tried to recreate the mechanics of the original game, but ignored the PvE side of things (always the largest portion of any MMO playerbase) in favour of really boring PvP which lacked the fun you want in PvP completely - at least for me and my dozen or so friends who had played DAOC religiously for about 5 years. Warhammer had some interesting features and classes, but not that interesting.
WOW - well I can't comment on this title at all since I have so studiously avoided it. I played it in beta and concluded it was MMO on easy mode and it was not that fun. The "ironic" modern culture elements mixed into the game no doubt contributed to its success amongst those who hadn't played a real MMO but they completely turned me off. Didn't last the first 2 weeks of the game once it went live. I understand subsequent expansions all tended to make things worse for a lot of players. It was massively successful of course.