Serious thread necromancy at work today!
Revising my opinion from 8 years ago, I'd probably have to say that ELDER SCROLLS V: SKYRIM is my favorite game ever, with DARK SOULS II running a close second.
Funny coincidence - I beat Skyrim for the first time last month and also played through the Dark Souls trilogy in the past couple of months. I didn't quite dig Skyrim as much as most, but it's still something I'd recommend for anyone who loves digging into lore heavy settings and messing around with TONS of options on a character in a game.
Dark Souls though... All three are great games. If you can handle the difficulty and the relative lack of hand-holding, they're extremely rewarding, deeply atmospheric, and exceptionally immersive games, and I'd list it as one my favorite series of all time now.
I had played the first game before several times, but never got too far. I think they have a significant barrier to entry. I might suggest reading beginner tips for anyone trying to get into the games, at a minimum just reading what the stats actually do and a few things like that, as some of the core mechanics are poorly explained.