I really like the idea of this thread, some good ideas coming through from people.
I've played WoW for quite along time and have certainly found quite a few flaws that could be changed for other games.
First, I would reduce the effect gear has on your gameplay, in WoW it makes far too much of a difference, not much skill is involved, skill should be a much bigger part of the game.
Another thing that needs changing are the raids, WoW's raids were excessive, most people do not want to spend 5 hours every evening (!) in an instance trying to get one item, most of the time they dont even get anything. Even if you do want to spend that long in an instance, it certainly isnt healthy.
I would either reduce the size of instances considerably, or do something similar to what Warhammer Online are doing, and make huge 'public quests' out in the open where everyone can join in and be rewarded for their effort.
Looting is a big problem in WoW, 25-40 people in a raid, spend 4 hours to kill one boss and 3 items drop :/ Now, everyone spent time and effort to kill that boss so why shouldnt everyone be rewarded for it? Maybe not all getting an item, but each discovering a quest after killing the boss that each player can do individually or as a group to obtain a reward.
Graphics wise, I found WoW to be OK, maybe a few slight improvements could be made, Im looking forward to Warhammer online to see what it brings. The Burning Crusade killed the game for me, I just found the new environments and areas far to dull and boring, like they had been thrown together in a day or two, I mean Shattrath was appauling, it looked horrible! Make the environments interesting and lively!
I like Spirity's idea of having a sport, that sounds like a great idea.
"No levels, everything is skill based. Everyone starts out with a basic skill template, and you cherry pick abilities through quests, item drops, and certain named/boss mob kills (you absorb a portion of the mobs power)."
I really like this idea, but Im still quite fond of the levelling process, I find it can be more enjoyable and more of an achievement when you gain a level, maybe the 2 ideas could be intertwined somehow.
I agree with Colinuk when he says its annoying when NPCs know exactly where you are when you attack them from a distance, that should be changed.
Totally agree with Spirity on changing the 'kill 20 of these and get me the paws to prove you've killed them' quests. As in Warhammer Online, the game should track what you kill , so if you come up to an NPC that says "I want you to kill 5 bears." and you have already killed 5 before you spoke to him, he will say "I see you have already killed 5 bears, heres your reward." Thats what I want to see.
Factions, I like where WoW was going with these until I found how insanely long it took to get Revered/Exalted, and how there were little/no quests to do it with. Factions should be fun to gain rep with, there should be quests and a storyline with each one so that you dont have to kill 500,000 tigers before youre exalted.
Loot should definately be fun, like Spirity said, less with the powerful gear, more with the fun.
Yes, titles should be hard to get, possibly related to the faction rewards, it shouldnt be the case of a 5 minute quest, then you're suddenly 'Thiras, the mighty bear-slayer' the titles could be funny, but they need to be hard to get.
I think there should be many many more secret quests that you sort of stumble upon when youre out exploring. Most people in MMOs now just rush through the game to get to the end-game bit, but a lot of the fun is along the way. There should be quest hubs in major towns in an area, but also a significant number scattered around the area too.
Thats pretty much all I can think of for the moment

