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.
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.