Another aspect of the 2d20 System is its focus on mechanics rather than roleplaying. It constantly reminds players that they are rolling dice, focusing their attention on decisions like, "Do I need to purchase Threat so that I can roll more dice?'
I personally don't see that as a bad thing. The idea that roleplaying and mechanics are these mutually exclusive presences is anathema to the way I think. You can roleplay without rules. You can game without roleplaying. Surely RPGs are the point where you do
both?
With 2d20, no only are players focused on dicing, but also the GM cannot easily hide the difficulty (as the AC is hidden in the Mongoose d20 game). That's a curse many roll low systems have. Players know their target numbers and instantly know whether the task was successful. Any GM commentary describing the scene usually falls on deaf ears because the players already know the outcome.
But, if you hide the difficulty, the player rolls the dice....and the GM can re-focus them in the game world, living through the character, seeing what he sees, feeling what he feels.
I also don't feel that "living through the character" is the be-all-and-end all of the RPG experience - I'm much more a fan of the author-stance than the actor-stance for RPGs these days, where the player is more akin to an author controlling the character, than a presence embodying the character (indeed, I tend to find that 'living through the character' tends to result in a number of problematic behaviours, where the player's attachment to the character makes them actively avoid risk, peril, and compromising situations).
This is likely a significant point of conflict here - player-as-author tends to see players more willingly putting their character into difficult or perilous situations, because they want to see how the character gets through them. Player-as-author also tends to be a lot more forgiving of metagaming, because it assumes an existing degree of distance between player and character. Player-as-actor drills down into "player choice must always equal character choice", which I don't regard as being particularly advantageous, outside of some forms of traditional gaming (even though, original D&D, characters were reportedly regarded as more akin to playing pieces, as befits units in a wargame).
With 2d20...they already know, and the GM is just wasting his breath, on most accounts. The players know the outcome and are looking on to what's next.
Except... not. Because hitting the difficulty isn't the end of the test like it is in a d20 system game. Momentum adds variety of choice and variation of outcome after the roll. Hitting the difficulty gives you the absolute bare minimum successful result... getting Momentum, from extra successes rolled, from using the group's banked Momentum, from bonuses like talents turns success into "yes, and".
With average tasks, you're less likely to fail outright... but often, the extras you get from Momentum are valuable enough and interesting enough (and impactful enough on the narrative) that their presence or absence changes things.
It's worth noting at this point, that I tend to take a very positive approach to player character success: in short, player characters are skilled professionals, and they
will succeed. With any given task, a player character will succeed given sufficient time and attention. Failure is the point at which opponents and obstacles interfere with the PCs.
To give a common example: the thief is attempting to pick a particularly complicated lock. Given enough time, he'll succeed, so long as he's allowed to concentrate. In a gaming context, he may fail if he isn't given sufficient time, or if he's distracted by some external force. The thief didn't outright fail to pick the lock... he was interrupted before he could finish because he heard a guard coming. The warrior didn't miss, his enemy turned the attack aside with a deft flick of his blade. The same applies to major NPCs - they'll succeed unless the PCs stop them. I don't fail to tie my shoelaces, but I might have to leave them undone because I'm about to miss the bus.
Consequently, the basic conflict of "pass vs fail" means little to me.
One thing to remember is that the system's designer was Jay Little, who designed the FFG Star Wars games. The two systems take a similar tack - the basic "success/failure" paradigm is a small part of things, and the extra things a roll of the dice present are a more interesting part of the game, and contribute more to the ongoing narrative.