When playing in a TTRPG, how important is immersion -- defined vaguely as "inhabiting your character inhabiting the world" -- to your enjoyment of the game?
It depends on the RPG. If playing a "light" (as in "light-hearted) game like (say) AD&D Against the Giants, not very. Character doesn't matter in a game like that, and my approach will be entirely about how much effort I put into the tactical/"how can we win" aspect of play.
I've also played my few 3E sessions in this sort of way.
But in what I would think of a serious RPG, where character matters, then immersion - what I would normally call
inhabitation of character is something I care about. This requires a RPG that aligns my play experience and motivation and orientation with the experience and motivation and orientation of my PC.
There are three main contexts where I've experienced this:
(1) Playing Call of Cthulhu one-shot railroads, where the GM is a skill evoker of images and emotions, and the descent into insanity is nicely scripted so that I can play that out in cooperation with the GM's narration. The
insanity trajectory is what permits the alignment I described above - I don't need to
choose for my PC, but just emote and portray a scripted path. This can be a lot of fun.
The risk to immersion here is poor scenario design, eg that suddenly requires me to make a decision as my character that risks derailing things, or to introduce a situation (say, a fight) that involves some non-emoting performance from me as a player.
(2) Nicely done one-shots where the characters and the situation mesh well, where the GM has the skill to frame the situation in an evocative way, and where the situation provides an opportunity for the players, as their PCs, to do their thing. In these games, it is that last thing that permits the alignment of player and character - everything that precedes that final situation is a build up, where we all poke around and build up our picture of our characters.
Immersion will be spoiled, in this sort of game, if there is a railroaded resolution to the situation, so that my attempt to express and realise my character bumps into barriers - eg the GM or the scenario signalling that I should do
this thing rather than
that thing despite that making no sense for my PC.
(3) An ongoing version of (2). Given that it's ongoing, I would expect to have a bit more control over establishing my character. And this also means that the GM's approach to creating situation will have to be different, if the sorts of barriers I mentioned aren't going to come up.
In my personal experience, the best RPG for this is Burning Wheel.
Do you endeavor to experience the world of the game through your character and only your character?
I don't really get what this means.
The only sense I can make of "the world of the game" is
the shared fiction, and I experience that through my experience of what others says and (much less often) draw.
Inhabiting my character depends on the fiction that I engage with going well beyond my character. (Unless my character is a solipsist, I guess, but I've never tried to RPG that.) My character has motivations, orientation, comportment, etc and there are many parts of the fiction that are integral to these.
Do you act, speak and even think as your character for the duration?
The actions I'm performing, when RPGing, are mostly talking. The thoughts include a range of things - certainly not limited to the fiction (eg if I have to roll dice, I'll be looking at them, counting numbers, etc). So it wouldn't be possible to act or think as my character does.
For my part, I don't only say things as my character. I will talk to other participants, about the play of the game and perhaps about other things (eg if they pass me some food I will thank them).
Do the rules matter for this, or is it more about the nature of play at the table? Are you okay seeing the sets and strings as it were?
Mechanics are fundamental, and likewise methods of play. If the rules, or the GM's methods, throw up the sorts of barriers I've described above, then inhabitation is wrecked.
A light-hearted game of the sort I described at the top of this post doesn't even pretend to give the character meaning. Eg Why are we fighting the Giants? Because that's the premise of this particular adventure.
What I find frustrating is a game that
pretends to make my character important, but really is one where the decisions I am required or expected to make are not ones that can genuinely flow from my character. "Plot hooks" are a common manifestation of this.