B/X: It was my first taste of ttrpg-ing, and boy was I hooked!! As a total goob for swords and sorcery type stuff, this was right up my alley.
Likes: Simplicity! The entire game: spells, monsters, rules and all fit in one well organized pamphlet. AND it worked very well! It was very easy to learn, so getting friends, relatives, etc involved was quick and simple. FUN to play. Served as a good stepping stone to AD&D, if you wanted to get further involved, or wanted more options.
AD&D 1E. I should note here, that we never really played by the "official" rules. We were in high school then, and arbitrary limits or clunky systems rubbed us the wrong way. Race class/level limitations went right out the window first thing. Encumbrance, non-weapon proficiencies, morale, etc went unused. Our version of AD&D looked an awful lot like B/X evolved, lol.
Likes: The Artwork!!! Both the line drawings, the cartoons, and the paintings were appealing to us. I STILL find the picture of the armored knight jumping into the wizard's arms- because rust monster!- to be hilarious. And, no, our table of teenage/20 something dudes did NOT scream like little girls when our DM sprung one of those monstrosities on us... Why would you think that??
The modules! So many fun classics. The tables. No matter what, there's undoubtedly a table for it. The fluff/lore.
MM II Fiend Folio; Unearthed Arcana. I found the cover art on the Monster Manual II to be especially evocative.
So much of our classic gaming is tied up in this edition.
AD&D 2E: Again, we didn't really play this as it's own system- to us, it was just an expansion on 1E.
Likes. Almost 100% backwards compatibility with 1E. When in doubt, we went with the rule that worked better for us.
The core rulebooks were much easier to read.
More everything: More spells, more magic goodies, more campaign settings, even more races and classes. They kept churning out more monsters, too. Speaking of which, I really liked how detailed and lore-ish the monster descriptions were. Splatbooks that added a lot more depth to PC races.
2E also had good, "classic fantasy" art.
Dungeons and Dragons (aka 3rd Ed) This version re-introduced me to the game. And also coincided with my acquisition of my first PC and internet access. The second thing I found on line, was message boards. And I joined every D&D related one I could find! Those were the days!
Likes: What the??!! Were Monte Cook and the guys hanging out watching our games back in the old days?? This looks a fair bit like our old game! Just with a LOT of cool additions.
Goodbye forever to "One Pump Chump" first level Wizards. Cantrips finally started to come into their own, and actually added something besides minor parlor tricks to the game.
Racial class and level restrictions? Buh-bye!!! 3E made our take on it official. AND came with a system for multi-classing that made sense. Rather than restrict demi-humans, to create parity with humans, they gave humans advantages of their own, bringing them UP to the level of the others. (ie the carrot, not the stick)
Sorceror class. An alternate take on the arcane caster. Perfect, fluff and crunch-wise, for adding to monsters- to give them magical firepower of their own!
They took the bard. and actually made it into a real, cohesive class.
The Cleric!!! Wow- someone finally made this class cool, interesting, varied- and FUN to play. Some of my favorite, and most memorable characters from this era were clerics.
Forgotten Realms Campaign Setting. And the subsequent regional and other expansions. Now THIS is how you do a campaign setting! They really brought this world to life, in my imagination. Great artwork, too. The 3E era was a golden time for campaign settings in terms of quality, imo.
The D20 system. Took all the weird, disparate systems of the old editions, unified it all, and wrapped it up with a nice little bow.
The Open Game License. Genius idea! Don't have the time, staff or budget to redo a bunch of old campaign settings? Let some other company do it! Same for alternate flavors, adventures, rules expansions etc. There were a lot of talented people putting out a lot of great material explicitly FOR the D&D game, or using the D20 system. Allowed WoTC to focus their energy on a small number of campaigns and core rules.
5E. Took an even bigger step towards our old games- the rules lite feel, and ease of play/introducing new players.
Likes:
Removed a lot of the rules bloat and numbers power creep. This version has more of the feel of B/X with all the best ideas from the intervening years added in.
It's even more of an integrated, unified system than 3E. It all works pretty well together, too- which is important.
Arcane Traditions/ Domains/Archetypes. Really great ideas for advancing characters, while adding in the best parts of feats, prestige classes, etc- without having a bunch of extra systems. I like how domains give you cool things to do with your channel divinity ability. And how Arcane Traditions really do make different wizards different.
The magic system. Cantrips as at will spells? Great! And they scale up with level? That's cool too! Casting spells using higher slots to boost their power? Works for me, too. Spells like Shield now being reactions to counter an attack being made on you. NICE! Even cooler that it dovetails with my Abjurer's protective ward ability. (saved his bacon a time or two!)
Advantage/Disadvantage. Simple and elegant.
THE ART!!! Wow, did some of these guys knock it out of the park!!!
That's so far. I'm just beginning to wade into this edition.