So in desperation, I finally broke down and actually looked at the D&D Starter Set I bought some time ago and, the more I looked at it, the more I liked it. The seriously-flattened power curve (referred to in the development process as "bounded accuracy," a term which only the most diehard grognard could like) makes the entire game world a much more level playing field: a rabble of goblins are still dangerous to high level PCs, and at the same time, low-level PCs are able to contend with more powerful monsters (if they do it smart and probably bring along some backup). Magic items, while still around, have largely been rebalanced so that they are beneficial but not "without this, you will fail"... the "PC wealth by level" guidelines are a thing of the past.
From a worldbuilding point of view, this means you are no longer expected (or required) to tailor the setting to match the PCs' level and capabilities. DC 15 to kick in a door at 1st level will still be DC 15 to kick in that door at 20th level. A horde of marauding goblins remains a dangerous threat for everyone, and a horde of marauding giants is a disaster. If there should be owlbears in those mountains, go ahead and put in owlbears, and if there should be wyverns, go ahead and put in wyverns. Let the encounter tables fall where they may! While 1st-level PCs are still very fragile at first, by the time they get to 3rd or 4th, they should have a pretty good feel for what they can and can't reasonably expect to do, and plan accordingly.
This means, when creating a scenario or filling a dungeon, I no longer have to carefully craft it by the numbers. Where I once used to map out "I need a 250 XP encounter in this room, which will award 200 GP, and a 500 XP encounter in THAT room, which will award 800 GP worth of potions..." I now can simply say "There should be some orcs in here. Bam." This takes me back to earlier days of gaming, in all the best ways. If the PCs are brawny fighter types, they can slaughter the orcs. If they're sneaky rogue types, they can trick or sneak past the orcs. If they don't want to go down that hallway, they can ignore the orcs entirely and I can pull out one of my "emergency backup encounters" instead.
Furthermore, at the table most modifiers, conditions, and the infamous "buff round" are mostly gone, thanks to the core mechanic of advantage/disadvantage, and the concept of concentration spells. Also gone are most attacks of opportunity, and with them the bajillion feats based on same. All the play reports I've read keep marveling at how much faster the new edition of D&D is. Granted, that's mostly comparing it to 4E, which was often a terrible slog, but that's also in comparison to 3.x/Pathfinder as well. You don't spend time counting fifteen buffs/debuffs to come up with a net +2; you don't spend so much time carefully planning out movement to avoid attacks of opportunity.
Of course, this is all behind-the-screen stuff; I have yet to see how I'll like D&D 5e as a player. What I've seen of character creation seems pretty flexible and cool: besides your class, you can also use Backgrounds to customize, you can multiclass if desired (if you meet the prerequisites), and starting at 4th level you can opt to take a feat instead of a stat boost to dip your toe into other classes' or races' abilities or to refine a particular character concept. Since my thing is always building characters around a concept instead of just choosing from column A or column B, I'm hopeful. Sure, the granularity of 3.x/Pathfinder made for all sorts of finely-crafted-character-honing, but you know, it also made building characters a nightmare that required an app to do with confidence.
From my initial reading at least, I feel like I could run or play D&D 5e entirely on paper and be fine. You get your stat bonuses and your proficiences, and you're pretty much done. The most complicated math is in the encounter XP calculation process.
So, as I say, I'm pretty jazzed about trying 5e out, and that's a nice feeling after being so frustrated for the past several months. I hope it goes well! I'll let you know after Saturday night. ;)