I think that looking at examples of games along the lines that you’ve described would show some key differences.
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I think your list of priorities shows that although both games may foster immersion and both present challenges to players, which of those things is prioritized would be the key difference. There would be other differences, too, and also many similarities, and of course everyone’s game is different, so there’s no universal answer....but where a game’s priority is placed is the big factor here.
One could quibble endlessly about the exact details of these lists, but it's definitely interesting to think about. I think I'd put immersion above challenges for myself, generally. I also don't so much "enforce" the rules as much as being a rules resource (since I usually know them better than my players).
I agree with
@hawkeyefan that it makes sense to tackle this by looking at actual games and the actual play of those games.
For me, what makes a game immersive is that the stakes and consequences are
compelling, and that
I can experience them directly through the play of the game. This works on either side of the table.
Here's one example that I pick because I hope it's easy to communicate: when we play Prince Valiant we use dice rather than coins (most of us use evens as successes; one uses 4+ on d6s). When there is a joust on, the typical pool is 6 to 10+ dice. When you pick up a pool of that size and start shaking them in your hands, it's like the thunder of hooves as the two knights charge towards one another! And then when the dice hit the table, there's that moment of suspense just before the impact and then you can see who's won and whose been defeated and perhaps unhorsed.
Here's a different example, that also involves jousting in Prince Valiant. Sir Lionheart, who claimed to be the greatest knight in Britain, was blocking a bridge to the north of Castle Hill. He would cede the brige only if defeated in a joust. Naturally the PCs rode out to challenge him! One of the PCs was only a squire, but - after the knight PCs had both been defeated - was able to manipulate Sir Lionheart into knighting him so that he too could joust. (Prince Valiant resolves social conflilcts just like jousting and other conflicts, ie via opposed dice pools.) The player knew that Sir Lionheart's jousting pool was big (having been at the table to see the other PCs bested) and knew that his own pool would be modest (the character emphasises the social side of things a bit more than the martial). But he had, in hand, a "Storyteller's Certificate" that allowed one use of a fiat ability from a list that includes both Knock an Opponent Senseless and Kill a Foe in Combat.
So as we were rolling our pools he was also deciding whether to use his certificate - yes, he would - and which option to go for. He didn't want to kill Sir Lionheart, but he was scared that if he only knocked him out then when Sir Lionheart regained consciousness he would insist on continuing the fight on foot, and perhaps to the death - and the player didn't have a second certificate!
Now I know some people assert that these sorts of meta-abilities break immersion, but for me at least it wasn't like this at all. The player's thinking about how to play the game at this point correlated pretty directly to the PC's experience:
I can't defeat this knight except through some uncontrollable luck. I wouldn't want him to die - he's a valiant knight - but unless some misfortune kills him he'll either win the joust, or else insist in continuing on foot and win at that point. And just as the PC wants but doesn't want Sir Lionheart to unluckily die, so the player reluctantly but resignedly plays his certificate - as we narrated it, the PC's lance shattered on Sir Lionheart's shield and a splinter went through his visor slit and pierced his eye and brain, killing him.
That was immersive, and the whole situation was surprising to everyone at the table: the PC who started the campaign as a squire, with the lowest standing and cheapest gear of all the PCs, was knighted, and defeated the best knight in all Britan, and as a result took possession of his fine steed, excellent armour and bejewlled sword.
For me what spoils immersion is (i) a sense that the game is already written, and (ii) a sense that the action is all happening offscreen. This is as much true for me GMing as playing - because as a GM if what I'm doing is (i) bringing my prior authorial decisions to bear and/or (ii) manipulating fictional elements in my head that no one else even knows about, then there's no sense of immediacy, of being there in this mutually-generated situation and experiencing it as it unfolds. Which is what I love about RPGIng.
