The problem is finding a balance between time invested and rewards. Lets look at some of the games leading up to where we are now:
UO : IMO the best MMORPG EVER! It allowed the most freedom, had free pvp, and though early UO took god awful long to GM a skill you were not useless until you did GM it. It had a completely player based econemy, grouping or solo both worked. You had status, bragging rights, and skill both in pvp and pve was a factor. Later on they sped it up to tailor to a younger audience which had no patience to spend 3 months to GM blacksmithing, if not longer.
EQ : Decent game, personally I am a fan of UO gaming style (later employeed by SWG but badly). Levels are ok but with such a large range of levels, especially for pvp, you were catagorized and then twinking became a major factor. Pvp was a joke it was built on a game not designed for pvp, thus no balance of any kind. Items you'd never lose (save RZ server), this was your reward for time spent. I liked UO's system better, it made it a player market that made tradeskills viable but you have to have it. Have to have something that says "Ive played this game longer then you and it shows."
SWG : Good concept, but the game moved TOO fast... there was no balance, UO type skill tree's (which I really liked it allowed no 2 chars to be the same) the problem was that there were super powerful templates (as is bound to happen sure) but there were too few of them. Only a few set templates really worked VERY well in pvp. You reached end game too fast (First month of game release I mastered armorsmithing and had way too much money, by 2nd month I was master doctor/swordsman and just about explored the entire game).
DAoC : This game at release was one of the WORST, I played Hibernia, and we didnt even have itemized dungeons beyond our first 2!! Realm balance was non-existant. They have gotten better, items are not permanent, but the end game ones you really worry about dont wear out fast enough for it to be a concern. My main qualm about DAoC as a pvper is that there is no risk to death, you die, you come back and have your buffbot rebuff you, run out and kill kill kill. UO you lost all on your corpse, EQ you had to CR which may take a while, SWG your items decayed alot unless you spent money to insure them to only decay a little.
L2 : Lineage 2 has to be by far the WORST game ive ever played, I admit I only played it for 2 months but its insane. The rewards for time spent curve is HUGE... levels take FOREVER to attain especially later on, the game is based on farming money to buy super expensive items that you can possibly lose when you die. Nothing like being a noob, buying my first Tears of Eva and then losing it to a bad pull 20 mins later... it was all my savings. The pvp is a joke and all about gank and oportunity. The farming is insane too, I would spend hours finding a group, only to get into one and find there is a group of adena farmers at our camp, mostly bots, protected by a few high levels. The ammount of adena farmers is insane at every level, I found some in elven ruins!!
WoW : I cannot comment on how the farming will affect this game, Blizzard has done a good job though of keeping the game smooth so far, im a lvl 20 warlock and must say ive not had to stop and farm money for long just to stay competitive. The quests are very fluid, and abundant, and useful. Ive yet to experience the pvp, and because I dont want ot invest alot of time in somethign that'll be reset at offical game release ive not tried tradeskills but they seem nice. I also like the talents, im not fully sure how it works or how many points you get how often, but it allows for some uniqueness.
Online gaming has come a LONG way since UO, I am that old vet who sits in his rocker reliving my glory days, and belive UO was quite possibly the best MMORPG ever made at its prime (after trammel it went downhill). :)