I have had more thought on this threads question to steer us back to why we all believe, or not believe, in tradition being important instead of blaming which edition sucks.
* Moving from one edition to the next edition should be without having to repurchase all the core books again. Each new edition should be creating newer expansions to support the core books. Why are we relearning the game each edition?
* Polyhedron dice, primarily the d20.
* Character sheets.
* Module maps inside cover and sleeve becomes the DM Screen; no need to purchase a new screen everytime; this was unique to D&D.
* Inserts: Tomb of Horrors had it right when the image art was separated into a booklet, similiar to today's Encounter Cards that fold over the DM Screen from Beadle and Grim.
* Original class titles: the fighter, magic-user, thief, and cleric.
* 4 player group (depending on the DMs skills, I have had one player at one time and 8 players many times, with a party of many others viewing it all on the sidelines.), with 4 classes balancing out the adventures.
*HD represents the Challenge Rating of a creature so an actual CR Stat is not needed.
*THACO (Since 3e now THAC10)
* Sitting around a table - not virtual, not at a con, but in a basement. It's that atmosphere that is intimate, private, secretive, and away from spectators.
* More roleplaying, light rules.
Keeping traditional tools, mechanics, structure from edition to edition helps share experience from one generation to the next generation and bonds everyone to the same rules we can all relate to one another.