What it is not is a grind fest, which is why people tend to like it, and I guess others who enjoy the grind don't. I played it for about 3 years, thru every campaign expansion. It is, IMHO, one of the best MMORPGs around. It is designed specifically so you don't have to grind, and the developers are ver involved with the player base and doing what is best for the game and players, and not themselves.
While all the towns and outposts are real time, all the combat area's are instanced. So everytime to leave town, you get your own instance of the game. Basically you put your party together in town then set off to go do something, whether it be a quest, mission, or farming in your own instanced world.
The game can be done solo if you wish. You can add hero's and henchmen to your party if you don't feel like playing with anyone else, or add a couple here and there, so there's no waiting hours and hours to put a party together just to do something.
What makes it different from other MMORPGs is that level and equipment are not as important as skill and game play knowledge. This game is very much based on strategy and less on high levels (the level cap is 20) or armor and weapons as the best armor and weapons are easily acquirable.
Instead of overpowered equip, GW features more artistic equipment. Your characters looks and higher price armor set the prestige and something to aim for after you complete a campaign. After you 'think' you finish the game, there's a whole world of things to do, titles to aquire, armor and weapon arts to seek, not to mention re-play value of the game with a different class is very high. I've beaten each campaign on about 6 different characters, everything is was enjoyable and not stale or boring even after doing it again and again. Each class offers a totally different type of gameplay.
GW2 is set to release sometime in 2010. It will feature more real time environments mixed with instanced game play. Currently, since I have already gone thru just about everything in the game I'm taking a break from it till GW2 is released.
I sound like an add for guildwars, but it really is a great game.
Oh yeah, then there's the whole PvP aspect of the game which is all about skill and not about level or equipment, again as to avoid grinding. You can hope right into PvP from day one.