Recommended watching/reading:
- The Skinner Box. Basic introduction to operant conditioning and games.
- The Overjustification Effect, or how too much reliance on extrinsic rewards can make an activity less fun.
Briefly, activities can have both intrinsic and extrinsic rewards. Intrinsic rewards are things such as immersion or the joy at overcoming a challenge; extrinsic rewards are things such as loot, XP, and status.
Games do not necessarily need extrinsic rewards to be fun. Tetris proved to be very addictive in its day, with little or no extrinsic rewards.
The excessive reliance on extrinsic rewards is relatively unique to progression-based MMOs (inherited from D&D). This can have deleterious effects in that players start to pursue activities that they do not actually enjoy anymore (see also: grind, burn-out), and gets to the point where even enjoyable activities become less fun because of extrinsic rewards. Few players in WoW have been doing dungeons for fun the past months; they are solely driven by VP, JP, or trying to see a piece of gear drop, as they kill Archbishop Benedictus for the 30th time while watching TV and complaining in guild chat about the morons that the dungeon finder put them in a group with.
That does not mean that extrinsic rewards are evil; but depending entirely on it for player satisfaction is a dangerous path to tread. (It is also very expensive in terms of development, since you constantly need to put out new content as old content becomes obsolete.)
What you need for a game that people keep playing without extrinsic rewards is to, first and foremost, provide content that not only is fun the first time it is played, but can be played again and still remains fun the second and third and fourth time. You then don't have to depend on extrinsic rewards to provide a carrot.
Now, not everyone will enjoy GW2, and that is perfectly fine. If you try to appeal to everyone, you will please nobody. ArenaNet is a business, they don't need to appeal to 100% of MMO players; 10% would already be several millions of players. It's better for them to entertain 1 player well than to entertain 10 players poorly.
That said, GW2 has a few features that help:
- Variety of content. Because you don't actually outlevel content, you're not just stuck with the level 80 game. That means that content does not become stale as fast and don't have to string players along with extrinsic rewards. ArenaNet will still have to push out new content, but they don't have to be as aggressive about it as Rift (note also that even Rift introduced mentoring recently).
- A strong focus on immersion (to the point of discouraging players from watching the UI as much as possible). Rich lore and beautiful visuals are intrinsically rewarding for a great many people. You don't have to be a hardcore roleplayer to lose yourself in a world -- ask any person who lost track of time reading a book.
- An active combat system. Games that engage the human mind's pattern-matching abilities tend to be more fun than those that don't. Note that it does not have to "hard" to achieve that (as ill-defined a term as "hard" is). It just needs to engage the human mind's proclivity for pattern-matching and puzzle-solving (again, see Tetris; not a complicated game by any means, but people still kept playing it).
GW2 will definitely lose players who will miss a progression-based endgame. But it will also retain a number of players who hate the grind aspect of progression. By focusing on the latter type, it avoids competing with Blizzard and Trion on their home turf, and instead creates a home for players to whom the progression game does not appeal.