Victor Gijsbers writes:
Immersion might be helped by not having too much rules stuff in play, but I actually don’t think this is very important. It is easy to drift in and out of immersion. You can immerse one moment, do some complicated rules stuff the next, talk about stakes the next, and immerse yourself back in. Please take care to notice that in my Polaris analysis, one fails to immerse not because one has to do things that don’t correspond with character actions; no, one fails to immerse because the character makes his/her important decisions and has his/her strongest feelings while the player is involved in something else entirely. If one’s important decisions all took place in the free play stage, immersion would not be hurt at all. (Of course, one should also stop playing Polaris in that case; it wouldn’t be helping you at all.) (http://gamingphilosopher.blogspot.com/2005/12/immersion-and-imagination.html)
To consider some issues presented above, I think that we need to consider imagination, rules, and the rule system of a game in more detail.
Vygotsky argues that “play involving an imaginary situation is, in fact, rule-based, play.” (1978, p. 94.) I tend to agree with this. Characters and a game world creates rules for role-playing. They are not that kind of explicitly formulated rules as the rules of a game system. Moreover, above-mentioned kind of tension between system driven play and imagination driven play is, I think, sometimes necessary for making decisions as if the character: the player’s values, habits, and goals sometimes tends to overdrive character simulation. The explicit rule systems (e.g., frenzy rules in Vampire) can push characters to do actions that are not obvious or natural to the player and thus be import part of character playing. While explicit use of resolution system brings the player apart character engagement or engrossment (I prefer these terms over immersion, see my post Role-playing and Immersion (and its alternatives)) they also give new grounds to character engagment after resolution.
While I disagrees with Gijsbers about his view of rules the blog entry contains otherwise insightful analysis of character engagment.
Vygotsky (1978). Mind in society: The development of higher psychological processes. Cambridge: Harvard University Press.