Off the top of my head:
- written by Erik Mona and well-set in Greyhawk
- excellent dungeon design, with a variety of twists/surprises
- expandable scenario if you include the "continuation" of the level into "A Gathering of Winds" by Wolfgang Baur
I remember liking the design of the cairn itself quite a bit as well.
I agree with all of that. It was just well written and had a certain mood about it. Not to mention Diamond Lake was well thought out. All in all it really was just a well thought out and well written adventure.
Lost City is B4, but still a great scenario, and one of Tom Moldvay's best!

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.