AD&D was sooo much more complicated that the Basic and Expert sets, but I was really glad that race was no longer a "thing" in itself - or that Elves were so much slower in their XP progression.
I was listening to a review this week that pointed out some of the parallels between The Keep on the Borderlands and The Village of Hommlet, which I'd never noticed before.
I really liked how well fleshed out the village itself was - names of villagers, the different personalities. The moathouse itself was always interesting, as was the final protagonist, Lareth the Beautiful, but there wasn't a lot of it - which can be a good thing if you're not wanting to spend too many sessions on it.
The rogue in my group loved his slippers of spider climbing and thought he'd avoid the cockatrices by walking on the roof - in a 10' x 10' corridor, though, they could still attack someone on the roof because they're in an adjacent square: the thing flapped up and struck him anyway, and he was turned to stone. It really established a tone for the group and my friend's power gamey but sometimes getting it wrong sort of method.
My main hassle with it was there was such a big gap between this and The Temple of Elemental Evil - this was a 1st-4th level adventure, and the other was a really high level 10th-14th level type adventure, I was never sure what the party should do in between. Lareth was a great opponent, but they would have forgotten all about him by the time they came back around to the same theme.