Now this is an interesting question. RPGs are definitely my favorite genre of game, but when and how often I replay them rather depends on the game.
For the Knights of the Old Republic franchise, I thoroughly enjoyed the story and quests, with even just one small side-quest still sitting in my memory as the Best. Quest. Evar. But as much as I liked it, I haven't really found myself able to replay it. While the story is fun, it is mostly simplistic; a celebration of the classic Star Wars experience without much else to it. On top of that, the player's 'choice' is just a binary equation of completely good, or completely evil. And not even that. The most gut-wrenchingly saintly Jedi that ever floated an inch off the ground, or the pettiest bully ever to wring his hands with spiteful glee. You could vary up your choices, but the game didn't give you any reason for that. As far as I could see, the game didn't even give you any reason to be evil, either. Just psychotic, spiteful behavior with the flimsy justification of a few extra credits.
KotOR 2, on the other hand, I have replayed half a dozen times. Despite the blander levels and comparative lack of polish, I hold it to be a superior experience. There is a deceptive amount of depth to its gameplay, but especially in its story. Despite the nonsensical ending, the morality at play is much more interesting. You are allowed to be the saint or the psycho, but you can also be a good person doing bad things for good reasons, a bad person doing good things for bad reasons, and many combinations. While Light and Dark Side points were doled out, very few quests would have the one simple 'good' and 'bad' decision. This has been the only game where I have been able to play an 'evil' character, because with the choices I am given, that behavior actually makes sense. And while the various companions might have been somewhat less loveable than the first game, I appreciated that I needed to win their trust before they spouted their life-story to me. And there is of course no way to gain full influence with them all in one playthrough.
For Skyrim, I did my usual Bethesda RPG routine of playing through the main quest once through to learn the ins and outs, and then again as a much slower, considered experience at harder difficulties. I like to be able to make informed decisions about my character build, and which quests I take when and how. It also allows me to go more in-depth with the persona of the character that I am roleplaying. Since then I've played through the main quest one more time, and invested about 300 hours over the period of a few months. But I have found myself coming back only occasionally. Skyrim provided me a short, intense burst of enjoyment, but I haven't found much in it to lure me back.
And then... Morrowind. My first love. My personal best game of all time. That I bought more than two years ago, and I continue to come back, playing nearly every day. The depth and richness of the lore, the interesting narrative for quests, the gameplay structure, the exploration, the magic system, the reading, the armor-design, and even the combat gameplay is all perfect for me. Certainly the game has many flaws, but all this and more is corrected by perhaps the most amazing modding community in gaming. I've probably played through the entire main quest with its expansions plus one entirely fan-made expansion over a dozen times now, most often with the exact same character. And no matter how many times I play, I always seem to find something new.
