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This is just my opinion of course, but this is the way I've seen the MMO gaming timeline, positive points only.
I skipped games that I know other people will add. Most major ones I've at least tried, but thought they just had a slight spin and didn't make my list. AO, SB and a couple I didn't even try though might belong on the list but I don't have the experience.
UO (1997) - Sandbox gathering/crafting + PvP = Good System
EQ (1999) - 3rd Person PVE - Big quests, big bosses
Runescape (2001) - Web based MMO (didn't play)
DAoC (2001) - RvRvR still sets the standard
EvE (2003) - Sci-Fi MMO in UO pvp/gathering vein
SWG (2003) - Sci-Fi Character customization/sandbox/housing/skills
WoW (2004) - huge and polished PvE
GW1 (2005) - Arena combat - 2 class system -buy then play free
AoC (2008) - Directional combat
Darkfall (2009) - Archery/Magic targeting
Aion (2009) - Flying
GW2 (2012) - Underwater combat
These are the games I felt formed the MMO field for me, except Runescape which I added because my son played it and then started trying web games so I thought it was important. I didn't point out what I felt like were negatives, but each game had their own negative points too.
I've tried a LOT of other games along the way, but I didn't feel like they added all that much to the field.
I still think EQ was the best of them all. Not just because of the rose color glasses thing, but the way they tried to make every level enjoyable and challenging and didn't look at early levels as just something to slow down players so that the content lasted longer.
Asdar