5e did what I would have thought impossible: the people that preferred 4e to earlier editions largely liked it, the people who were repulsed by 4e but stayed with 3e/3.5e or forks of those liked it, and a lot of the “old school” crowd that preferred OD&D, B/X or BECMI D&D, or AD&D 1e or 2e also liked it.
> Why would someone who already knows AD&D 1e switch to the new one? What does that person gain?
Aside from network effects, the rules are much easier to use in play without referencing fairly arbitrary tables; there's a lot of streamlining and consistency that lets them handle more situations with less lookups, different mechanical subsystems, and fiddly bits.
Notably, a unified success mechanic that covers skill use (including what were “thief skills” in core 1e, as well as “nonweapon proficiencies” from some of the 1e supplements), attacks, ability checks, and saving throws is a big improvement from 1e (D&D has had that in some form since 3e, though.)
the short answer is that some systems better support creative experiences than others.
Each system provides both power to tell stories and restrictions on what stories make sense within the framework. 3.5e, for example, was a high-powered but extremely clunky framework -- it let you build epic creative experiences, but often got in its own way. 4e was a lower-powered storytelling experience because it was so focused on "balance". (My experience doesn't go all the way back to 1e so I can't comment on its specific strengths and weaknesses.)
One thing I really like about 5e is that it's quite streamlined, but has a variety of options integrated into the core game. Things that were clunky in prior editions (like prestige classes in 3.5, or ritual-casting in 4e) are now supported smoothly. So it's high-powered but also kind of gets out of the way.
EDIT: I think the fear of learning new rulesets is itself a reaction to the overly complex early-edition D&D rules. You have to learn so many different types of mechanics and try to keep them all straight. You have a bunch of different bonus types and have to learn which ones stack, and then try to maximize the overall stack. 5e is actually really quick to learn, and as such, it gets out of the way of the creative storytelling experience a lot more than earlier editions.
> 5e is actually really quick to learn, and as such, it gets out of the way of the creative storytelling experience a lot more than earlier editions.
To add to this, one minor thing I like about 5e is how much freedom the game explicitly gives the Dungeon Master. Obviously nothing is truly different, the DM is god in every edition. But I've played with many, many DMs (usually new DMs) who will refuse to do something fun because it goes against some way a rule is written in the book. Even if they and the whole party wants it to happen, it would be breaking "the rules".
The first DM I ever played with actually would never let us call anything a rulebook. It was a Player's Handbook or guidebook, or what have you. Because as she said, she was the rules, not the book.
I think that really helped form a mentality of "Fun First" when I run a game. The 5e books felt a little heavy-handed at first, every third spell says something along the lines of "If the DM chooses". But it's already helped me in some real games as a player, where the DM can do what they want and not what the book says, because by doing what they want they're still doing what the book says.
The biggest gain: A much larger pool of potential players/DMs. If you limit yourself to other old farts who still have their battered old AD&D 1e books then that’s a pretty elite set of fortysomethings - my D&D Blue Book and my set of AD&D 1e is long gone, after three cross-country moves and one hurricane.
Also 5e is AMAZING for giving out a TON of story hooks as part of the character creation process. Sure, you and your GM may be old pros who know how to make a story, and that’s great. But if you’re having an off day, or bringing in some new players who don’t know how to prepare the seeds of a story, it’s pretty damn useful to have all these hooks lying around.
Everything is generally streamlined, you will mostly be rolling a d20. Other dice show up for your HP and damage, because it’s just not D&D without that handful of weird-shaped dice.
> If you limit yourself to other old farts who still have their battered old AD&D 1e books
AD&D/1e (and other pre-5e versions) books are available in hardcopy and PDF, new, today. There's certainly a network effect benefit to 5e today, but 1e isn't limited to people with battered copies from the 1980s.
FWIW I've had more Dungeon Masters/referees for Lamentations of the Flame Princess (a modern horror-themed retroclone of the 1983 Mentzer D&D Red Box) in my home city than any other edition of D&D or any other tabletop RPG.
You can get rid of THAC0 if you just use this simple rule: roll d20, add the opponent's armor class (plus your own to-hit bonus if any), and a result of 20 or better is a hit.
3E's Base Attack Bonus was mechanically identical, but expressed in an easier-to-understand way. Briefly, they rearranged things so that higher numbers are always better--having +1 armor no longer means you subtract 1 from your Armor class.
For me, nothing. I play 1e (and have played 5e et al). Pick the one that gets you excited. If you like the art, the names of the monsters, and the community, those factors outweigh any minor differences in rules or organization.
It's similar to programming languages - there's an ineffable quality to a language that makes you just want to use it (or not). I knew someone who picked up DarkBASIC several years ago; I could have suggested he get into Python or something more "mainstream", but I think the right choice is the one that makes you want to sit down and work on your project.
Pathfinder still has a dedicated following though - maybe that's the one niche (tons of detailed customizations and third party add ons) 5e didn't fill?
Sure. I'm not saying 5e killed every other D&D and clone system, just that it seems to have come done a good job at appealing broadly to what had become a very balkanized fanbase with separate communities that were hostile to each other's preferred systems.
