Every massively multiplayer online Role-Playing game that has ever existed has always sucked, sucks, and always will suck.
The most obvious reason for this results from the formula of the gameplay, which is caused by an inherent economic problem, which itself stems from the very essence of what it means to be an MMORPG. Read on to understand all of this.
In most multiplayer games, there is no goal: You play for the sake of the match; when the match ends, you start another match. When you stop playing, you're satisfied because you just had fun.
In most RPGs (Conventional ones: Level up to increase your stats, encounter monsters randomly, fight in turn-based combat, etc.), you strive toward an ultimate goal while becoming more powerful in order to match the power of the opposition to your goal. At the end, you're satisfied because you just completed the goal you've been working to achieve for the entire game.
What's a multiplayer RPG? Leveling up for no reason? An online multiplayer game can't have an ultimate goal because then the goal is achieved and the game ends for everyone, and standalone matches don't work in an RPG because the level-up system makes it unfair for the less powerful players. It's just leveling up mindlessly until the maximum level is reached and all the quests are completed, at which point the game is done and the player is left with a feeling of wasted time.
MMORPGs try to fix this via an update system. Usually this means that new content will be routinely added to the game, with the hope of keeping players' interest even once they are "done".
Sound premise, but now comes the economic problem...
How are these updates paid for? A game can only be sold once, but routine updates are indefinite. An indefinite monetary source must be found... Makes sense to ask for money from the PLAYERS, right? Yes, and indefinite money for indefinite updates sounds like a good trade-off, too... But it doesn't work. Players still get to the top and feel "done".
So what do the designers of MMORPGs do about it? Restructure their games: Most notably, make everything take longer (so getting to the top takes longer.) This is where the first gameplay flaw comes in: Rewarding time more than skill. In a skill-based game such as Halo or Super Mario World, a very skilled player can rush through a level and beat it in 3 minutes, whereas a very unskilled player will fail constantly and only win after retrying for a long time. However, in a TIME-based game such as Runescape or World of Warcraft, any player will have to spend hours increasing a single level regardless of his/her skills because that's just how long it takes, and it won't take any longer for unskilled players because it doesn't take any skill to begin with!
Prove me wrong! Just name an MMORPG and explain how the combat works (if there is any.) If it's fun, you've proven me wrong!