Every game has a level of immersion, some more than others. This is hardest to do in an MMO, where eveyone has their own playstyle, and a game can quickly turn into an OOC (out of character) bitchfest in game forums.
I'm thinking a lot on my Darkfall experiences for this one. A common recruitment hook for the Goons was that Hyperion roleplayed, and thus were fags. With the horrible chat system, most people couldn't even communicate before they started killing each other. The only game 'immersion', was the competition between players, making it an entirely OOC affair.
I'm wondering how Xsyon will work out. Will it feel like my character Baldur is murdering this guy named Joe in cold blood, or will I just be ganking some noob? Will there be thought out tribal politics, and diplomacy, reputations... and rules to make it so?