I think a lot of the old adventures stand up better now that I'm an adult and understand how the game really works than they did when I was a stupid kid and ran/played them the first time. We had the notion that every module (with a couple obvious exceptions, like The Assassin's Knot)should be played as a straight-up slugfest -- bust down the door, kill whatever you find, gather treasure, go to next room and repeat until there are no more rooms or you have enough xp to go up a level (or maybe if you're so low on hp that you're about to die, but that's a sign of weakness). This endless succession of huge fights led to two things: 1) DM cheating in the players' favor, both by fudging dice-rolls and by playing the monsters "dumb" (e.g. not reacting to the sounds of a huge fight in the next room over); 2) players' obsession with buffing their characters -- obviously if you're going toe to toe with level 4 of the Temple of Elemental Evil, or the Forgotten Temple of Tharizdun, or the Steading of the Hill Giant Chief, you're going to need a lot of hp and a lot of heavy artillery (i.e. magic items), so you eventually end up with a party full of munchkin tanks loaded down with a couple dozen magic items apiece.
I suppose you could say that we weren't really playing "wrong" because we had a lot of fun playing that way for a couple/few years, even if we did eventually get bored with it and move on to other, more 'serious' rpgs -- RuneQuest, Call of Cthulhu, Traveller, etc. -- but what became glaringly obvious when I began to re-read the rulebooks and the modules with 'fresh' eyes and an adult persepctive is that, whether we were having fun or not we were playing the game wrongly, and that the supposed 'problems' that led us away from D&D weren't intrinsic to the game itself but rather to the way we were playing it (although the fact that TSR was also cheesing up the joint with their 2E mess right around that same time certainly helped drive us away...).
It's made abundantly clear time and time again in both the rulebooks and the modules that the way to play the came smartly/successfully (i.e. well) is to be careful and plan ahead, use tactics and trickery to avoid or nullify encounters without direct confrontation (combat) whenever possible, not be distracted from the ultimate goal, and to know when to retreat and regroup when you're low on resources or have encountered something too powerful to handle. Looking at a module like The Steading of the Hill Giant Chief with these considerations in mind it suddenly makes much more sense -- the 'correct' way to succeed at that module isn't to have characters tough enough to take out Nosenra and his entire court all at once, or a DM willing to cheat on their behalf, but rather to sneak around disguised as giant-children and avoid raising the alarm and having to fight all those guys in the first place. The intention is to challenge the skill and ingenuity of the players, not just to test the strength and mettle of their characters. Knowing that, everything that was once old is now new again, and feeling fresher and more intriguing and challenging than ever.
