Hmm, haven't played but two MMOs, Horizons and WoW. Did the EQ2 trial, though.
Horizons - I liked the crafting, and ability to be a dragon... many biped models were poorly animated, though, and had ugly emotes. The biped multiclassing was interesting, and I liked the playable Satyrs and Dryads. Combat system was very boring, and there wasn't any kind of organized aggro system, it seemed very chaotic.
However, having to make 8 sets of 600-900 crafted items for one LOWEST LEVEL ROOM of dragon housing, burnt me out. Spending 4-6 hours grinding digging holes in a sandstone field sucked, and there was really no combat goals. Few world bosses or events. Most loot was craft components. And I did like to craft, but... too much grind. Also, the world is very big and empty.
Entire stretches of continent and NOTHING there. Pretty scenery though. Very small population meant I was alone almost all the time, 90% of the playerbase is max level and doing their own thing. I got lonely and tired of working so hard on a dragon house, that nobody would see or care about. Without any kind of decorations or furniture, it would just be bland storange space, and nothing personalized.
I met some very nice folks there, however, mostly bipeds. I found many Dragons to be very elitest and rude to new folks who didn't follow the oldtimer's personal views of 'how to play'. I reget not playing on their non-RP server, since it had more then 3 times the population and probably more liveliness. Maybe that would've changed my overall impression.
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EverQuest 2 - Played the trial. The colors and models of the world and characters were very sterile. The emotes my Ratonga had looked unnatural and some were downright scary (like /dance). Nothing about the play-mechanics had that 'spark' that would've made me stay or be interested. It felt very 'machine-made'. It had no personal, overall design theme or aesthetic. I think they confused 'realism' as equalling 'colorless and bland' design.
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World of Warcraft - My first MMORPG. What got me interested was playable minotaurs, frankly. Before, most MMOs seemed to have either only recolored/resized humans as 'races' or else ugly (to me) models. As an animation/graphic design major, I liked the style and look of the game, the way they had set color-schemes, etc. for each zone, and the little details and humor that showed an obvious love by the art designers for their work. Perhaps having had training in graphic arts helped me appreciate the qualities of 'cartoons' which many people just dismiss as an inferior medium. Yes, it's exaggerated and not photorealistic. But it pulls off it's -intended- style the way it was meant to, and very well. I also like the emotes, the way a character will animate 'speaking' when you type, and laugh and such. I hate characters that just stand motionless and have no life outside of combat. However, the total lack of meaningful character customization, especially at the the creation screen, is very disappointing.
I like the combat system, the way each class is very different yet powerful in their own way, and in the group mechanics. It's very structured in the roles, that I feel makes combat work well. I agree that too much of the game is soloable, many people never learn their group roles or how to even socialize, it seems, and make later-level 'pickup group' dungeon runs sometimes horrible, with people doing their own thing, being uncommunicative, and wiping the group because they don't listen to the leader or don't think to help others. It's ironic, because the ONLY level-cap content, raids, require precision coordination, communication, and strategy, skills which the other 99% of the game lets people get by without learning.
My guild is great, if it wasn't for that core group of friends, I would've left much earlier. They make the game fun, mostly I raid to hang out with them, more than for loot. I wish there were other things we could do. Without a guild of quality folks, it wouldn't be as enjoyable. The gameplay at lvl-cap is pretty much limited to dungeon farming for loot, and raids.
Crafting armor and weapons is mostly a waste, better gear is easily got in dungeons. Most materials to craft the few 'good' pieces are worth more to sell raw, than to use. Its obvious the craft designer never understood the things that 'hardcore' crafters love and why people like crafting in the first place. Crafting's more of a hobby than anything important ingame.
The WoW Expansion will probably determine how much longer I will play. If it addresses a lot of the weaknesses of the current game, I will stay longer. I'll hate to leave my friends, but I'm kinda getting bored. One can only make alts for so long before stuff gets monotonous.