Second edition Advanced Dungeons and Dragons is perhaps the most disliked version of D&D (though 4E certainly has its critics). This wasn't always the case. Hatred for 2nd edition wasn't universal in its heyday, in fact between 1989 and 1997/98 most gamers I encountered actively played 2E. I was no no exception. But these days the edition has a reputation for railroading and story focus, and many people hold it up as an example of bad design (or at least bad GM advice). And this criticism is valid. But 2nd edition did some things very well. So lets not throw the baby out with the bathwater and dismiss everything that arose during the 2E era.
Since attacks against it are directed at its spirit, I will be defending the less tangible aspects of 2E instead of defending its mechanics. The reason for this is it had much in common with 1st edition, many of the changes it introduced were already existing houserules or options, and I recently defended many of its key rules in my blog on unified mechanics.
Clearly, second edition came from a time when story was prime. There was a sense in much of the game material in the late 80s and in the 90s that the GM was the author, the players his protagonists. This predates 2E with the Dragonlance modules and setting. However Dragonlance transitioned into 2E smoothly and many of its underlying assumptions carried into other second edition material. You also see this with Vampire, D&D's biggest competition at the time. I would argue that you can chart TSR's emulation of White Wolf as the 90s progress. The emphasis on story in 2nd edition grows as Vampire's popularity increases.
But RPGs are not books or movies. To achieve the kind of story TSR suggested, the DM needed to railroad, fudge and fiddle with player freedom. I just ran a bunch of 2E Ravenloft modules and there are plenty of instances where the writers suggest railroading or fudging for story purposes. They even suggest making key NPCs immune to death in combat. In some cases the modules are even structured into three acts with scenes. I readily admit this advice was bad. Not only does it work against the rules the designers themselves created but it gave people some whacky ideas about GMing. With that said I would argue that 1) GM advice is easy enough to overlook and 2) In the case of 2E it is worth overlooking because there is so much cool material. And oddly enough much of this material stems from their misguided focus on story.
The one thing everyone generally agrees 2E got right is setting material. In the 90s we were literally buried by the volume of modules and supplements devoted to their numerous campaign settings. You had Ravenloft, Darksun, Dragonlance, Forgotten Realms, Spelljammer, Planescape, Birthright, Kara-Tur, Greyhawk, Maztica, al-Qadim, and a few I may be forgetting (can't recall if Savage Coast was 2E or basic). Granted, some of these began as 1E settings but the important thing is you couldn't count the available worlds on one hand. Plus there were numerous variations like Masque of the Red Death.
Personally I gravitated toward Ravenloft and owned every book released for the Realm of Terror. I would site the Van Richten's Guides (to vampires, lycanthropes, ghosts, the created, the ancient dead, liches, vistani) as examples of another (related) thing 2E did well: flavor material. These were, in my opinion, some of the best gaming books ever written. The Van Richten Guides inspired me as a GM, they showed me how monsters could be used creatively, how investigations and monster hunts might work, and they helped give me a micro-level appreciation of the Ravenloft setting. My games thrived in part because I read the entire line of Van Richten releases. As with setting, I believe one of the key reasons these books were made is because of the focus on story.
Roleplaying and immersion is another area whre 2E (like 1e before it) excelled. They introduced non-weapon proficiencies, but these were unobtrusive enough that you still focused on what your character said and did rather than roll for social interactions. So when I went back to playing Ravenloft 2E, after years of Ravenloft 3E, I immediatey noticed the level of in-depth role play increase (something I had remembered but chalked up to nostalgia). Because there was so much focus on worlds and interesting characters, I think the emphasis on role play was natural.
Though 2E is attacked for some of its bad GM advice, it actually had one of the best DM supplement lines, the blue books. Things like Campaign Cartographer, Creative Campaigning, The Castle Guide and The Villains Handbook were great resources for GMs. These were packed with great information on everything form mapping to player types. I still use many of the prop and mapping techniques discussed in Campaign Cartographer.
It also had a whole line of green books for various historical settings. If you wanted to play a Roman game, there was a green book for that. Renaissance Campaign? Viking Campaign? Knights of Charlemagne? There were books for these and much more.
I could go on about the brown books and their kits, or 2Es naturalistic and historically grounded spirit, but that would lead to more talk of mechanics than is my goal, so I will close with praise for their modules. It is true, 2nd edition modules suffered a lot from the story focused railroading. But they alsonhad a lot going for them if you look past this (and in practice I find it easy to do). Since I am most familiar with Ravenloft, look at Feast of Goblyns and Castles Forlorn. These were solid because they provided lots of interesting setting material and mixed it fairly seemlessly with adventure and characters.
Feast of Goblyns was the first module I encountered (though I am sure it isn't the first module that did this) where the NPCs were treated as free agents who moved around and reacted organically to the PCs. I believe they called it a living adventure, and I still use that term to this day. This opened all kinds of doors for me as a GM, ultimately leading me to excel at character driven and investigative adventures.
Both Feast of Goblyns and Castles Forlorn had exciting locations you could strip out and use as needed. Famously Feast of Goblyns gave us The Kartakan Inn. A whole section of the module is devoted to it. But it also gives full descriptions of two towns (Skald and Harmonia), a castle, a lair, a homestead and other places.
Castle Forlorn Provides a much needed overview of the domain of Forlorn and a massive description and map of its castle. It was a non-linear adventure, more like a setting book with a bunch of hooks. So it had lots of backstory, characters, creatures, etc but not much in the way of linear adventure.
So yes, too much emphasis on story, fudging and railroading were bad, but I think our memories get clouded by these recollections and we forget much of the good that came out of 2E. In my opinion, it was the greatest edition in terms of flavor and setting. And even though they were bogged down by the spirit of 90s, the modules themselves were often very good if you could look past some quirks.