Don't make players talk to every NPC to find a quest. We try to make it easy to find the quests, a menu of options for things to do. There is a side effect, what we call the Christmas tree effect, which is too many exclamation points overwhelming the users. There's a balance between too few and railroading, and too many.
Give players a menu of options, but with a limit of 20. Raising the cap on the number of quests is one of the most common requests. We do have technical reasons not to, but the real reason is that the bigger the quest log gets, the less you feel like you are on a mission to do something. If you vacuum up the quests, and then kill indiscriminately, you are probably doing one of them. So putting in a limit makes people make some decisions.
Quest designers are 'the cruise directors of WoW.' Their job is to show you the world. When we first do a zone we talk about POIs, points of interest, how many of each type of quest, and that's the job of the quest designer. Different people like different kinds of quests. So we have to give you a list of possible entertainment to choose from.
Pacing: the bridge between depth and accessibility. Once you have all those deep features, then you have to figure out how you get from the newbie experience to that core experience. For WoW, that's done through the levelling curve. When I hire designers for Blizzard, one of my pitfall questions that I ask is 'why do you think WoW was successful'' One of the hidden answers is the levelling curve ' if you extend the levelling curve too far, it becomes a barrier. You hit a levelling wall. Our walls are shorter and there are less of them.
The short levelling curve also encourages people to reroll and start over. We had some hardcore testers who would level to 60 in a week. There was much concern within the company. But I would tell them that we cannot design to that guy. You have to let him go. He probably won't unsubscribe, he's going to hit your endgame content or he'll have multiple level 60s. In games with tough levelling curves, it discourages you from starting over.
Rest system also helps with the casual player who plays 4-5 hours a week. The hardcore player will keep the game in 'no rest' state the whole time, whereas casual players will get rewarded for weekend binges followed by days off.
Bite-sized content: we try to tune our quests for accomplishment in chunks. We aim for a 30 minute session, lunchtime battlegrounds. We are doing more 'winged dungeons' in the expansion, because we kinda stumbled upon it. We split up the dungeon into separate wings that can be done in 1/2 hour to an hour ' like Scarlet Monastery. This was a lesson we learned during development, so we weren't able to apply it everywhere in the original release. You want to avoid getting to a place where the content of your game doesn't allow people to play unless they have X amount of time that night.
We aimed battlegrounds at the folks who over lunch would play Counterstrike, or Battlefield 1942.
Concentrated coolness. What this means is, rather than make variety and lots of things to do, make fewer things really cool. The best example in woW is the class system. Lots of games have more classes, multiclassing, etc. We consciously avoided that in order to make each class as cool and different from the others as possible. This allowed us to have unique spells, abilities and mechanics. No red fireball, white fireball, blue fireball, etc. Even the two pet classes, hunters and warlocks, use their pets completely differently. We consciously avoided sharing mechanics across classes. We recently announced that the paladins and the shamans are switching sides. One of the primary reasons why we undid that rule was that we found ourselves merging them into each other for PvP balance. So we decided that it was less important for each side to have its own class than it was to have concentrated coolness for each class.