It's the closest thing to a genuinely new idea 5e has seen implemented so far.
I don't think that's fair. Both because advantage (as you point out) isn't really all that new; and because there are lots of other new-ish thing in 5e. Then again I don't think novelty is a laudable goal, here.
...
It's just a very player-positive mechanic.
That's a clever observation! Advantage
is rewarding to get. I'm not sure how big or long-lasting that psycho-trickery effect is, but it's an interesting perspective.
Bounded Accuracy has definite effects on the game, but they're mixed. It means anyone can try anything at any time, because the d20 is never overwhelmed by large bonuses or super-high DCs. It also means you can fail at something you're supposed to be good at at any time. It means the same monsters are still a threat in large enough numbers, even at high level, and that a party can at least put some damage on a higher level monster. It also means that your sense of getting 'better' as you level can seem minimal.
Effects are definitely mixed - it's a basic choice that influences all kinds of things in the way a campaign evolves. In general it strikes me as an aspect of the game with lots of upside, few downsides, but in any case with a lot of impact (in contrast to advantage, which is entirely unobjectionable, but doesn't change the game much). Even with bounded accuracy, I don't think that the sense of getting better seems minimal. In a way, bounded accuracy *enhances* the sense of progress, because it's actually possible to revisit old foes and see how much you've advanced. Unlike 3e and even moreso 4e, a significant level gap in a combat is still playable. I'd like to draw a corollary to your observation about advantage here... In all three editions, fighting a dramatically underlevel foe simply poses no risk. Even in 5e that's the case, because although attack bonuses etc. don't change as much (and they still do change quite a bit), hit points and other abilities do to such a degree that an encounter that was challenging at low level or even forced you to retreat will at high level be a cakewake. The point is that even though there's still a huge power gap as levels rise, the fact that low level creatures can at least make a dent makes a world of difference. Instead of a boring, onesided fight in which only one side ever hits and it's just a question accumulating enough damage, the fight may involve an actual exchange of blows - it's just that the higher level creatures will shrug off piddling damage they receive, and the lower level creatures will be blown to bits. Also, the fact that *groups* of creatures do provide a threat mean that you can really showcase to players how they've advanced. Whereas early in their campaign they might have needed all their strength to take down just one ogre, at level 10 even half a dozen will be much easier (and in my experience the DMG slightly exaggerates the extra difficulty of multiple monsters, so I'd expect an actual level one party to have much more difficulty dealing with 1 ogre than a level 10 party would have to deal with 10 ogres, even though the encounter building guidelines suggest otherwise). Player's love encountering foes that (nearly) bested them and teaching them a lesson; and bounded accuracy actually makes those encounters playable.
On the topic of magic:
It's not reasonably balanced with the non-caster classes. Balance isn't a hard-coded thing in 5e. It's a roving spot-light largely under the DM's control.
I'm not sure what you're getting at, but it's reasonably balanced in the sense that the DM doesn't need to try hard to keep all players relevant. A wizard doesn't render a fighter moot, nor the other way around, even if the DM isn't paying too much attention.
Seriously, lack of differentiation and variety is a good thing? I can see how magic being a fungible, consistent, known-quantity in the setting would evoke a sense of verisimilitude or 'connection to the world,' but it'd also undercut it feeling, well magical.
Any system of player magic is going to undercut the "magical" feeling in the way you describe. Magic is almost by definition unexplainable and unknown, and a player-controlled magic is kind of the opposite. But I strongly disagree with the notion that 5e's system lacks differentiation. Differing PC's don't have identical magical repertoires; they build it from identical components. Even in 3.5 the average spell tended to have multiple nearly identical copies with minor, boring differences. And 4e took this notion much further. It's not differentiation if all those spells differ in name only. I don't see the connection to verisimilitude, but the great advantage of a small
yet diverse spell list is that players get to know those spells well, thus tying them more deeply into the game - not least, the DM. That also lets the game designers get away with significantly more complex spells that if each and every class had all their abilities separately described. It's very hard to adjudicate a spell you've never really heard of, so naturally if the spell list is huge, the spells must be fairly simply and the DM interpretations more literal and less nuanced. It's also harder to balance, so if you're going to be designing spells by the thousands, there's going to be an underlying system. And if that's the case, you might as well codify that simpler underlying system, rather that waste all that valuable time, paper and player attention. So, it is precisely 5e's
small spell list that enable
greater differentiation and variety, not less.
It hasn't been this 'slow' since the early 80s, and, I have to agree, it'll help keep the game from collapsing under it's own weight the way late 2e and 3.5 did (well, for me - everyone has a different threshold of bloat).
Yeah. I'm not sure if you played 4e, but that was similarly bloated (almost 10000 powers, and over 3000 feats...). No idea how big 3e became by comparison, but Jabba the hut would surely have been impressed. Let's be honest, there's a good chance over the years it'll happen again to some extent, but for now, I'm pretty happy - and perhaps with this new caution, at least the worst consequences will be avoided.