They look, to me, like an array of random and/or largely repetitive combat encounters, occasionally interspersed with uninteresting puzzles.
Yes, I'm about to get lynched.But it's true; I've been gaming well over 30 years, and I firmly believe that a large number of the "classic" modules are considered good only because of when they came out, and really don't actually have nearly as much to offer as many people maintain.
I'm not saying that the "novel disguised as module" is the right way to go. But I think many of the shorter/classic modules go too far the other direction.
I played those modules when they came out. The reason they are considered great is all the magic in them with one caveat I will mention later for Against the Giants. Against the Giants has fairly fun and challenging combat encounters (even if they are repetitive), meaning lots of stuff to kill. Any time you wanted to outfit a character with some powerful magic, you run one of those two modules and you're set. Those items were so nice for that time. Against the Giants is one of the first modules to actually include a girdle of giant strength and hammer of thunderbolts in the module. The three named items in White Plume Mountain were awesome to have. Every Elric fan boy back in the day wanted Blackrazor. I remember those modules fondly because of the extraordinary stuff you got out of them. As a melee character, wielding a hammer of thunderbolts or Blackrazor was an awesome feeling.
The one caveat that makes Against the Giants a great classic is the surprise introduction of the drow with stats. It was quite surprising at the time when in the third module you're fighting powerful, magic resistant dark elves. Now drow are old hat and far, far, far less powerful. They were some scary bastards in that module. It went from fighting big, dumb giants to unknown dark elves that seemed to laugh at magic. If you can imagine a time when drow were completely unknown and you experienced them for the first time, then you understand why Against the Giants is a classic.