Just looking at my backlog of non MMO games, I don’t need to play any MMOs for the next 10 years. And being aware of the fact, that my backlog is actually growing rather than shrinking ... you get the idea.

I don't play any.

Multiplayer in general is not my style. I'd like to have a solid game experience at my own pace, so I stick to single-player games.

Only one i play is Star Trek online time from time.

In single player I can cheat to reduce the grind. in MMO I will be label hacker and banned. So I rather an offline Single player game that cater to my needs, after some coaxing with the game files.....

Using some mods will be cool too.

trainers for me
i fucking hate grinding its an archaic means of artificially extending the life span of a title when space was a precious commodity

these days we have hundered of thousands of mb's and games as big as 60 gig
and grinding is only there because its used in and mmo and because its so entrenched or part of the genre ( jrpg's )

its high time grinding dies rather sooner then later

I just want to have to pay for a game once, not every month or to progress. The closest thing I have played was Guild Wars, which is kind of like an MMO. I liked it for a while but got bored with it eventually. You level capped too soon and then it was all about the equipment grind.

Story was decent though.

I played Lord of the Rings Online from open beta for a coupl ed of years and loved it. Great mmo. But then I got married and found that the time isn't available for grinding, crafting, leveling, etc. Now single player is all I do.

Used to. Guild Wars and Guild Wars 2 are my favorite games of all time, but I don't have or want to spend the time on an MMO anymore. But I miss it everyday!

I played some MMOs but quitted them entirely as I can't stand constant changes in game rules - regular class "balancing", ability retuning, etc., and that's in best case. In worst case it is outright substitution of original gameplay experience (WoW's Cataclysm, RO's Renewal, SWG's NGE and so on).

Another reason - I want full control over the game experience. Subscription, always online AND relying on X other people to see all content - it is too much "no-go" for me to consider playing MMO.

Use to play World of Warcraft

used to play shooter games with garena, but stopped when their software updates gave me the finger. tried quake live but was bad at it, and its full features were only available to subscribers, so that's a killjoy.

also used to play countless hours of custom maps on warcraft 3. eventually got bored of it and lack of people playing anything else other than DOTA maps.
i felt the same way about WH40K: Dawn of War 1. relic just got worse at balancing their game with each patch. it seems to me they were randomly picking suggestions from their fanboys and nerfing everything they don't like.

I returned recently to GE after a year-long break. That's the only MMO I actually like, for while the game plays itself, I can do whatever I want, occasionally doing some quests or raids.
Also, I like its setting. I mean, settling the New World (yep, there are Indians there as well. Sort of. Later in the game) with mages and knights is fun as it is, but as you get new characters, your play-style may change drastically.

I don't play any multiplayer games.

Btw What is the difference between MMO(Massively Multiplayer Online) and a Multiplayer game?

EDIT:Other than MMO capable of supporting large numbers of players simultaneously in same world.

^ An MMO has a lot more players on a server. They can play together or do their own thing on the same server or in the open world, etc.

I played TERA for over a year. Currently I am playing only single player games, but I am waiting and watching MMO scene as I would like to go back to playing online some day. It's the kind of experience you never forget: the epic scale, human interaction, dungeons and bosses like none in any of the single player games, and so on and more.
I think about it everyday TBH. Single player games are fun, but they are short and never can be that complex and engaging as a game designed with hundreds or even thousands of hours of gameplay in mind. The amount of content in MMOs is staggering. This is a different league. So yeah, I am thinking a lot about how fun it was and that I would love to experience it again.
And if someone is saying that MMOs are all about grind or they are so boring that make them sleep, then I think they didn't play any good ones or simply do not know how to play such games.
I can give one advice: do not go into MMO with a mind-set you have for single-player games, because you'll miss a lot and won't like it.