How to Kill the Grind
Surely I'm not the first guy to presume to tell developers what I think they should do to reduce the grind feeling that creeps into most MMORPGs, but I'm going to write this anyway.
To me, the grind becomes notiecable when you begin to do the same thing in the same manner over and over again. Its great if PvE combat consists of taking aim, pressing a button a few times, then maybe using a special move. But when you do that again and again without the need or ability to change things up, then it becomes a grind. Kill tasks, delivery missions, and item collection quests are fine, but when you force players to do them over and over, while they fight recycled critters by pressing the same three buttons, then you've created a noticeable grind. So what can developers do to hide the grind?
Speed, variety, and balance, for me, are the keys to making the grind less noticeable.
A fast game will hide the grind behind a steady stream of quick encounters (when it makes sense). A fast game also has the benefit of making players feel powerful - we typically play heroic characters after all and, to me, its not heroic to slog it out with an angry boar for 30 seconds. A short encounter duration (the time it takes you to kill that boar) means that you're not standing in one place for a long time cycling your attack animation. It keeps you moving, which goes a long way to hiding the grind.
Balance also goes a long way to mitigating the grind feeling. If a game forces players to stop playing and start grinding, then its out of balance. With a few exceptions, when you're at a certain point in a game, you should be able to consume all the basic content that exists for your level range. A bad example of this kind of balance is WoW, which forces players to stop playing and start grinding faction just so they can gain access to a piece of content. A balanced game keeps players on track and gives them in a steady stream of achievement, and that helps the game feel less like a grind.
Even if your game is slow and unbalanced, a monumental amount of variety will keep it feeling fresh. Combat becomes boring when every fight is executed in the same manner - so add more critter behavior, animations, and abilities. Questing becomes boring when you're on your 10th kill task of the day - so add more and different goals. Simply exploring the game becomes boring when the climate and terrain doesn't change - so add points of interest and vibrant zones, and give players quests that make them experience that variety. Even gaining powerful items becomes boring if they look similar to another item you used 10 levels ago. Variety is king.
Of those three things, variety is probably the toughest one to get right. This is because its just so easy for developers to recycle content. It saves budget and gets the game done (and making money) much faster. Lack of variety is the biggest reason I've canceled my subscription to every MMORPG I've played, including Tabula Rasa and City of Heroes.
In summary, I feel that a "grind-free" (players will always create their own grind) game is a game that keeps the player moving, provides many valid avenues of advancement, and that is always giving players something new. Will such a game ever exist? For some people it already does, but not for me, and not for all the gamers who constantly jump from game to game looking for one that finally gets it right.