Building off that WoW Add-On I mentioned in the previous section, what has happened in quest heavy MMOs is they are less about having fun and more about following a to-do list. You run around to the NPCs with yellow exclamation points, get your list of tasks, follow them in an efficient manner (with add-ons to actually calculate the most efficient path for you), then run around to NPCs with yellow question marks so you can turn them in.
The joy and wonder of playing a game in a rich, virtual world has gone by the way side. Instead, you are a low level bureaucrat filling out order requests and filing them at the appropriate NPC overseer.
When WoW implemented daily quests, I realized the industry was really going in the wrong direction. Daily quests are hardly different than a list of chores for some kids living on a farm. You login, you load up on your "dailies", and you grind them out for money and reputation. People do these exact same quests hundreds of days in a row. To make things worse, the culture of the game has devolved such that people averse to grinding out their dailies are called lazy. This is a game we are talking about, and people who are not interested in mindless, uninteresting, repetitive daily chores are chastised for their lack of work ethic. Sounds like a workaday, time punching job to me.
Quests are not a flawed concept. They can be an extremely interesting, fun, and engaging way for designers to tell stories and connect players with the game world. They can be used to create relationships between players and NPCs that actually seem meaningful. They can create the illusion of personality in major game NPCs. There is a lot of potential.
But when quests are overdone, or when quests are used as the main form of advancement, the system breaks down. All the flaws listed throughout this post become exposed. Eventually, players suffer the same frustration and tedium they complained about in pure grind games.
It is important to make players feel like their actions are meaningful in a game context. That is what tends to make such actions interesting on their own, rather than interesting only because of the loot or xp they give. If people care about what their character is doing, they will enjoy it regardless of the reward. This goal has to be approached from multiple directions. There is no single, absolute way to make content engaging. Quests are one way, but only when used in moderation.