10SKYRIM SPECIAL EDITION
I mean, you knew I was going to include this, didn't you? We're going to get the Bethesda ones out of the way right off the bat because it's a given that they were going to be included. Skyrim is one of the most engrossing and humongous RPGs ever released.
It has a ton of replay value, it has a ridiculous amount of decisions you get to make, there is so much depth when it comes to building your character, and the world is full of characters who are (generally) interesting and fun to hang out with. There's a reason people talk about this game in hushed and reverent tones, and if you haven't played it yet, there's no better time than now.