For me, I think the perfect D&D lies somewhere between 5E and Pathfinder.
For me, "perfect D&D" is a contradiction in terms. D&D is, if anything, a game defined by it's imperfections.
I have been a DM since the 1980s, and I am thrilled with 5e. Especially the 6 saves, the spells, the lack of a christmas tree of items . . . but my players were unhappy.
I take it they didn't start as early in the game's history as you did?
Let’s start with my biggest gripe – the lovely backgrounds. Yes you know my problems with this – “You don’t limit your player’s creativity game” Yea it’s cool that your history matters but you just don’t. At least they are easy to make, but if you have to make 100 of them why don’t they just give you – Here this is what you can pick, mix and match it until you are happy.
At any given moment you'll need a maximum of 1/player.
And then they talk about personality – the fabled IBF. Here there be the basics of your character. This mechanic I’m sad to say is useless for us.
I question the wisdom of the 'carrot for RP' approach, myself. So, just don't use it. Fixed.
Fewer magical items you say, well that sounds good because before I used to look like a christmas tree whenever someone looked at me with detect magic. In theory it is fine, a great idea even, until you understand that you get them super rarely, thusly being unreliable reward.
I've heard (wohoo! hearsay!) that uncertain rewards are psychologically quite powerful.
what can I do with that gold? Buy ponies and that’s about it, can’t buy magical items, they are too rare, can’t improve myself in any way really, so I have more money than god and no way to use it.
There's not much you can spend it on in your powergaming wish-list, but who knows what campaign factors might suck up money. Re-building a ravaged town, fortifying a captured manor, currying political influence, etc...
downtime and social interactions and something that could be broth up but it has 0 mechanical support. I wish I had the DMG so I can really get to the core of these problems, but alas I have to just point some of them out.
AL has a some downtime ideas for you.
Finally I will tell you what I think about “rulings not rules”. I think it is lazy and uninspired way to pander to everyone. Well we didn’t want to tell you how to run your game so you decide. Sorry, but did I but a rule system or a guideline no how to create my own.
If you created your own game - and you were good at game design, it'd do exactly what you wanted. OTOH, if you use a published game, and just over-rule it any time it doesn't /accomplish/ exactly what you want, you may not have the perfect system, but you're providing your players the experience you might, had you such a system. An imperfect solution for an imperfect universe. The only downside is that such a game is only as good as the DM. Making the game better only somewhat alters that formula. A game like 5e is bad in the hands of a poor DM, OK in the hands of a competent one, and good in the hand of a great one. A game that is much better-written and balanced, OTOH, is bad in the hands of a willfully bad DM, OK in the hands of a merely poor one, good in the hands of a competent DM, and great in the hands of a great one.
But, the effort to design - and the increasingly group-specific appeal of - a 'better' quality game makes it hard to create one that people don't get passionate about, including some really, really hating it.
My own PF game just ended at 10th level, and it was a slog to get that far. To be fair, a bit of it was my own fault (I allowed for half-or-better on hp rolls), but come the end nothing short of CR 17 was challenging 5-6 10th level PCs. This was do to a good combination of teamwork and and some broken parts of PF (a summoner who usually had his eidolon + 1-2 cannon fodders soaking up attacks, a gunslinger/rogue who never missed due to touch AC, a cleric who usually selective/quicken channel burst to keep hp high, A paladin that nuked anything evil from orbit, etc.) In the end, I could only run a decent fight if verged on TPK or took several hours for the PCs to break through the foes defense systems. It was very unsatisfying and more often then not felt like the combat metagame was the important part, story came second.
I'm hoping 5e makes this more manageable, because the effort I put into making PF fights work vs. the ease they got slaughtered in a hail of summons, smites, and gunshots was pathetic.
PF still sounds like 3.5, I guess. While not to the extent 4e did, 5e does make encounter creation easier than 3.5/PF. It's still tricky, you can certainly have a tough fight turn into a rollover, but at least you didn't put as much effort into it's creation, and, you also get the reverse, for variety. Mainly, though, the big difference is on the player side, you won't be seeing PCs as game-wrecking as PF, or even as 3.5 core-only.