Interesting question there Caio.
I confess rp in games isn't something I specifically look for. When you've rp'd a tabletop gm who will tailor the world and npcs to your players, put in all the incidental characters from nemeses and rivals to shopkeepers and photographers, who will have an unfolding story that your players will be the heroes of, just playing one character in a huge online world with a static setup and thousands of other players where nothing is tailored to you is to me quite a come down, particularly since in a lot of rp enforced games it seems all the significant content and development goes only to a small bunch of players and everyone else is hanging on the edges.
This was very much the feeling I got in Hollow, dark grimoire and especially star conquest, indeed the latter really irritated me since for a hugely well written game with great single player activities and quests, being forced to rp by essentially being told to go and beg your faction when your ship gets blown up is just plane depressing! that doens't you feel part of a game world and community, it makes you feel useless!
This is why I tend to play games more for the single player exploration, the quests where my character can feel like they have a significant effect upon the world, and to explore, rather than to interact with other players and vaguely hope for something significant to do.
That being said, even though I don't literally seak for rp there are a couple of games where I've engaged in it by accident, usually when I'm doing other single player things, or because the games ethos encourages, rather than discourages that type of thing.
The first of these I'd recommend is Clok.
There the out of character and in character distinction can take a little getting used to, but I love the fact that to get a class you need to talk to people of other classes, and that even if your off in the wilderness doing extensive crafting etc, you still must interact in a very mundane way. If you've ever wanted to feel like you've journeyed across the wilds, come back with a huge sack full of stuff you've hunted or gathered, sold it off at the market, took a bath, got a hot meal and a bed and some company, Clok is the game for you. It's not exactly the sort of earth shattering rp where your character is the center of a story, but you do feel like your actually in a world, not just part of a gang of other players with a few significant ones.
Avalon the legend lives: This one is a little odd since they're policy on rp is rather more interesting as they don't have a strict ic/ooc distinction. They call it "realplay" this essentially means if you go on the newbie channel and say "I'm trying to work out how to gather fruit" someone will turn upp, teleport in and help you.
Avalon is also really nice for tying single player and rp activities together, being as you get quests from other players, forge items with them, even fight other players but only in context of fighting for your city or whatever, heck even learning activities is mostly done from others.
It's a huge game, my only major issue with it is that since everything is driven by interaction with others, frequently I'd finish the newbie intro and then say "hay what now?" if nobody was around to let me know what to do next, since it's a huge and complex game.
Oh and btw, don't be putoff by the fact it's nominally a pay to subscribe game. There is a really interesting system whereby someone, be it your city, guild, church etc will sponsor you as a player. This essentially means that as long as your active, you don't have to pay anything.
Actually Avalon is a game I keep trying to get into and apparently they've had a rebuild of a newbie introduction area recently so maybe I should give them another go.
The third (which might not surprise you if you've seen me raving about it), is flexible survival.
Here the the rp is rather formalised with a rigid ooc/ic descrinction, though it did rather irritate me that people rp'd on the ooc channel.
You can engage in what are called judged scenes, these work like rp sessions with a gm and several slots. You can also rp with others if they're hanging around. One rather unique thing is you actually get rewarded in game for rp, so you can actually progress your character, craft gear, get xp etc.
yes, given the nature of the game some of this rp, both one on one with others and in the scenes can be erotic in nature, but there are strict controls to set limits on that sort of thing, and both the hard coding of the game and the ethos of the community has very good etiquette to make sure you won't be asked to rp anything your uncomfortable with, indeed given how unreservedly weird some of the game (especially the single player game), could be, I was quite impressed with how welcoming, and none dodgy the community was.
hth.
I will also note there is rp on cosmic rage, but I haven't engaged in it, mostly there I've been playing around with all the cool activities.
With our dreaming and singing, Ceaseless and sorrowless we! The glory about us clinging Of the glorious futures we see,
Our souls with high music ringing; O men! It must ever be
That we dwell in our dreaming and singing, A little apart from ye. (Arthur O'Shaughnessy 1873.)