
Massively Online Multiplayer games are different. They are generally a social experience, meant to be played over long stretches of time rather than simply beaten and shelved. There was a bit of an explosion some years ago after World of Warcraft made the bankest of banks ever, and thus companies threw a lot games out there in the hopes of getting their own WoW money. So maybe you're new to this whole thing, and maybe a friend wants you to play or maybe your curiosity has gotten the better of you. Or perhaps you're a grizzled vet that, against your better instincts, has an MMO itch to scratch. Either way, this thread will serve as an aid for deciding which MMO to play. It seems to make more sense than having a player jump between 10+ threads asking questions.
This thread allows is for cross-pollination you may not get elsewhere. Simple comparisons that may be difficult to answer in other threads, or maybe you feel it'll derail the current conversation elsewhere. A good example of a post is "I like WoW's raid content, but feel it's lacking in casual stuff. How does SWOTR compare?" whereas a bad example is "Explain FFXIV's endgame to me." which would be better in, you know, the FFXIV thread. This also is not a chat thread where people get into pissing contests defending their pet MMO while attacking others. A good guideline is to ask yourself "Is this line of discussion beneficial to someone looking for a new MMO or am I just rushing to the defense of my game?" The thread doesn't serve much of a point if people are afraid to post because people are arguing about which grind for bear asses is less tedious.
In order to help people, this OP will serve as a collection of MMOs along with a list of features, cost, and prospects. It's not meant to be comprehensive descriptions but just a jumping board for people to find MMOs they want to research further. If you don't see an MMO on this list, then just post your own and I'll add it to the OP.
Also: discussion regarding private servers are against the rules. Do not suggest an MMO that was officially shut down.
Last Update: September 2018
I have removed Blade & Soul from the list of games as it doesn't seem to be all the popular in the community

Developer: Blizzard Entertainment
Released: 2004
Cost: $70 ($20 Base Game + Legion expansion)
Payment Model: Subscription ($15/mo; can buy sub time with in-game currency) + Cash Shop; Sub Time
Frequent Compliments: Massive playerbase, so you can normally find a group of likeminded people. One of the best leveling experiences out there, something that changed MMOs forever. Quick, fun, and catered to solo players, you will probably get your money's worth by leveling alone. Technically solid, with crisp responsive gameplay and loads of mod support for tailor-made UIs. Raids are considered high-quality content.
Frequent Complaints: Old, so the game may not look as good even with character model updates. Casual content is considered lacking, and the endgame is generally seen as "raid or unsub." Game has a history of very slow content updates, particularly between expansions where as much as a year can pass with no new content.
The Future: Battle for Azeroth, the newest expansion, launched in August. The first content patch is up for testing.

Developer: Square-Enix, but players will tell you Yoshi-P
Released: Originally 2010; A Realm Reborn 2013
Cost: $60 ($20 for Base Game, $40 for Stormblood + Heavensward)
Payment Model: Tiered Subscription ($15/mo at 8 characters per World or $13/mo @ 1 character per World) + Cash Shop
Frequent Compliments: Beautiful game with varied content including raids and playing dress-up. Job system means you never need to roll an alt and can play every class on one character. Crafting are treated like classes unto themselves, and thus can get very deep. Solid story experience for leveling with tons of stuff for Final Fantasy fans to geek out over. Some of the fastest content delivery out there, normally offering something new every 2-3 months. Robust player and guild housing.
Frequent Complaints: Combat may seem slower thanks to higher global cooldown on skills. Need to complete story before doing Heavensward expansion content (including access to new expansion classes; Stormblood avoids this), which can take well over 18 hours to complete. PvP is kinda weird. Housing can be very expensive, although you can buy a personal room at your guild's house.
The Future: The expansion Stormblood has been released, with regular content patches being released.

Developer: Arenanet
Released: 2012
Cost: Free; $30 per Expansion ($50 for both)
Payment Model: Cash Shop, but gems can be bought with gold
Frequent Compliments: Dispenses with the "holy trinity" of tank/heal/damage. Emphasis on builds over having 30 skills to remember. Excellent PvP, with both huge World PvP zones and special structured PvP battlegrounds for a more level playing field. Breaks up the standard MMO progression with no quests but rather events and special renown hearts that offer more freedom in how one levels. Living Story provides regular content updates. No real gear grind at endgame.
Frequent Complaints: The lack of holy trinity makes combat feel a bit loose and weird for some. Instanced PvE content is present, but added to the game infrequently. There is regular content, but up until season two all Living Story content was temporary. You have to pay for older story content if you miss it.
The Future: Path of Fire, a new expansion, a has been released with regular content updates.

Developer: Bioware
Release: 2011
Cost: Free ($20 for Shadow of Revan Expansion)
Payment Model: Free-to-Play (Subscription Benefits)
Frequent Compliments: Perhaps the best single-player MMO leveling experience out there, with Bioware copying WoW's general design and adding a class-specific story with dialogue options and full voice-acting. Subscribers can level purely off this story to cap without having to bother with side quests. Companions are characters that you can gear up, send on crafting missions, or assist you in general gameplay. Has special content like starship missions which are akin to Starfox-esque gameplay.
Frequent Complaints: Free-to-play model is considered among the worst in MMOs, with stuff like your quickbars being tied to the system. Voice-acted, but you will eventually noticed a lot of canned responses that get frequently recycled. PvE content is generally seen as good, but not quite as good as WoW's from which it heavily borrows. It's Star Wars, but Old Republic so your appreciation for the theme may be lessened if you're more a fan of the original trilogy than the Knights games.
The Future: A new expansion for Fall 2018 has been teased, but nothing concrete yet.

Developer: CCP Games
Release: 2003
Cost: Free
Payment Model: Free-to-play, with subscription offering numerous benefits
Frequent Compliments: Huge PvP focus, with territory shifting among player-created factions. Features like spies makes for very memorable moments in the game history as a major fleet is destroyed from the inside by infiltrators. Fun galore for those who love to craft and farm and play economics. A game for the space sim junkies out there.
Frequent Complaints: High-stakes PvP, as you can lose everything in particularly bad engagements. Pretty cutthroat in general, as there are plenty of stories of people being scammed out of loads of in-game cash. Not a game where you can make a group with friends and have an impact until you're willing to play with one of the big dogs. A space sim, so if you're expecting WoW gameplay then look elsewhere.
The Future: The latest expansion, Into the Abyss, was released this past spring. A winter 2018 expansion has been confirmed but is currently TBA.

Developer: ZeniMax Online Studios
Release: 2014
Cost: $60 + DLC packs
Payment Model: Cash Shop, Optional Subscription
Frequent Compliments: Good PvP that reminds some of DAoC's RvR. Interesting combat and class building. Has a good payment model, being buy once and forget it.
Frequent Complaints: PvE content was originally grindy and not very fun. Usual zerg pitfalls of world PvP if you don't have a good, coordinated group.
The Future: Murkmire, a new DLC pack, has been announced.

Developer: Funcom
Release: 2012
Cost: Free
Payment Model: Cash Shop
Frequent Compliments: Unique setting for MMOs. Story based game that some alternatives to combat for gameplay. Instead of leveling you unlock skills and abilities to make a build to beat up Cthulhu monsters with. Story is engaging with memorable characters and plots.
Frequent Complaints: Made by Funcom, so while not nearly as bad as Age of Conan, similar weaknesses may be present. Seen as rough around the edges in regards to polish and bugs. Quests can be confusing at times, forcing you to google answers.
The Future: Regular updates being released, with Orochi Tower due in October.

Developer: Bluehole Studio
Release: 2011
Cost: Free
Payment Model: Free-to-Play (Subscription Benefits)
Frequent Compliments: Frequently praised for having the best execution of "action" combat, which is where you aim skills and they have hitboxes instead of just picking a target and pressing a button. Popori are rad as hell. Armor that isn't pandering to teenaged boys is pretty and/or awesome looking. The kinetic combat combined with cool looking monsters makes for very engaging gameplay.
Frequent Complaints: Full of fanservice which can be offputting. Questing and leveling is nothing revolutionary, and the story isn't anything to write home about. There is a race aimed at pedophiles.
The Future: Dark Reaches update has been released.
The Graveyard
Sometimes you can't go home again. Check to see if your old MMO has kicked the digital bucket. Please note that, while we are aware of that some of these games still technically exist, discussion about private servers is forbidden.
The Matrix Online
2005 - 2009
Star Wars Galaxies
2003 - 2011
City of Heroes
2004 - 2012
Warhammer Online: Age of Reckoning
2008 - 2013
Asheron's Call
1999-2017
Asheron's Call 2
2002-2005; 2012-2017 (Relaunch)
Firefall
2014 - 2017
Wildstar
2014-2018
2005 - 2009
Star Wars Galaxies
2003 - 2011
City of Heroes
2004 - 2012
Warhammer Online: Age of Reckoning
2008 - 2013
Asheron's Call
1999-2017
Asheron's Call 2
2002-2005; 2012-2017 (Relaunch)
Firefall
2014 - 2017
Wildstar
2014-2018