I love how we have a lot of Skyrim players in this thread. In the interest of adding something that's not Skyrim (As much as I want to choose it), I'm going to go with Diablo 3. I have sunken so many hours into that game, my husband calls me a pigeon. (A really sly reference to the Skinner box where pigeons get a food pellet for pushing a button, (Laugh).).
Over the last month, I have been playing Final Fantasy XIV: A Realm Reborn, which has actually been a lot of fun. Where I have enjoyed many aspects of this MMO, including how professions and crafting are handled, the questing and advancement in guilds in required over simply leveling crafting and gathering as skills or something are done without wider engagement (Like in World of Warcraft). A crafting system that is easy to learn, but requires a bit more thought and consideration to master. In calculating the steps one will take to make high-quality crafts
More, even the classes and jobs in general, the use of roles as a party, and even how the abilities of each class/job are used. More, it is accessible to new players and isn't too challenging starting out. Where the balance well the story questline so that players can level their characters and work towards higher level play. The real challenge I have learned is in the dungeons and raiding, with questing to introduce you to dungeons and easing players into easier dungeons appropriate to their level. I'd argue, again, better than World of Warcraft. My primary experience in MMOs.
More, it is an MMO that gives you the tools and basic training in a job, as well as guild questing, to allow players to be eased into learning how to play their chosen job and in combat. There is simply so much to be impressed about, especially since you can level a job to 60 on a free account. Better because you can level each job to level 60 on a single character! This gives you plenty of content to play with even without a subscription. With I feel tighter and better writing overall, with so many things you are given to do as you play and level.
Though a few words of caution I might give, is to be very careful you are registering for a free account and downloading the free launcher. If you make the mistake of registering a full account and downloading the full game, the email you use for such cannot be used. Since they have free accounts and full accounts separate, you can upgrade free accounts to a full account (While not downgrading a full account to a free one).
I make that mistake when I first registered and tried downloading the game, that perhaps being my one primary frustration.
I could say dark souls was one of the games I played for half a year. The replayability and difficulty, couldn't get past at the bosses like ceaseless discharge and capra demon but the endgame value and finally getting to finish the game was worth it.
I've played Skyrim like that. Also Civilization IV (Although I haven't gotten into the later Civ titles as much) Mount and Blade: Warband (Especially with the Floris Mod). I haven't played video games regularly of late, so I couldn't name any newer titles I would play for months on end like that.