Personally I prefer a game that's just fun to play. Rewards are nice, but when they become the reason you're playing, that defeats the true purpose of playing a game. So it'd be nice if MMOs depended less on the crutch of rewards to keep people playing, but that requires actually developing some dynamic content. Admittedly that's not the easiest task when you're trying to get years of play out of a single game, but nowadays the hardware is more capable of handling diverse content. Bit of a tangent, but just to highlight that what I'm about to say about rewards is much less important than the actual gameplay (i.e., fighting, crafting).
Rewards are really only necessary to keep people playing once the play content no longer becomes fun. That said, given some need, or at least inevitability that there will be rewards, it's very important that they are carefully constructed and not too challenging to obtain. When rewards become too competitive and difficult to obtain, it fosters a climate that reduces enjoyment for everyone, both because of the negative peer climate, and because it increases the likelihood of inducing what's called the overjustification effect. For those too lazy to google it, basically it's when getting a reward for doing something actually makes you enjoy it less.
As far as rewards go, the only really important thing is that there is some consistent feedback for your progress. In FFXI, for example, this is problematic because feedback does not match progress well. Having excellent gear is generally the standard for feedback, but having excellent gear often does not convey competence. As a result, the reward process that drives goal development is poorly reinforced. i.e., you're led to develop goals that you think you want to achieve but end up meaning very little to you.
Bottom line there is that what players need (hardcore players especially) is a game that lets them develop their personal skills, and where the feedback (e.g., level, gear, rank) matches their skill level, not hours played.
Ok, now we're going to get slash fiction of Wint x Kachi somehere... rule 34 and all...
Never confuse your inference as the listener for an implication of the speaker.
Good games are subjective like good food is subjective. You're not going to seriously tell me that there's not a psychological basis for why pizza is great and lutefisk is revolting. The thing about subjectivity is that, as subjects go, humans actually have a great deal in common.