You make a compelling point.
Were there _ANY_ "classic" second edition modules?
The two best ones I can think of, Night Below and Dragon Mountain, suffered from some similar flaws to TOEE--they're simply repetitive and boring and almost impossible to keep the players interested throughout the whole thing. I ran Dragon Mountain for about a year, and even with an engaged group I had to cut out about a third of the last book. You can only fight so many cheese-tactic kobolds before you start getting bored. And I mean _really_ bored.
I like Carl Sargent's "City of Skulls" quite a bit, though I never got a chance to actually run it. Because it was from the short print run era at the end of the Greyhawk product line I imagine most people are not aware of this module, but it's one of the better ones from the edition.
Beyond that...
I like Monte's Labyrinth of Madness well enough, but a printing error actually makes the main puzzle in the module unsolvable, and it's more of a one-upped Tomb of Horrors than a classic module in its own right.
Any other 2e candidates?*
--Erik
* Please no one mention Terrible Trouble at Tragidore...
The ones you name are good candidates, and I'd add A Paladin in Hell, Axe of the Dwarvish Lords and Return to the Tomb of Horrors to the list. I think they all came so late in 2e's run that they could never get the traction to be viewed as classics; the advent of 3e overshadowed them.
A Paladin in Hell actually took an iconic D&D pic as its inspiration and came up with an adventure that takes the PCs into some tough, unusual adventure sites. Axe was, in my opinion, the best depiction of an abandoned dwarven city TSR ever did. Return to the Tomb of Horrors was tough and spooky.
I'll add that The Shattered Circle should rightly be considered a classic low-level module. It also suffered from appearing so close to the end of 2e and the beginning of 3e.
But since this is about the worst modules, I'll chime in with my candidates:
Gargoyle - Already mentioned, and I'll add that I looked at it long and hard to see if there was a way to rework it into something usable. Even given that I used to look at stuff like that as a challenge, I just could never see how to make it into something I'd want to run.
Castle Greyhawk was a shock because instead of delivering the module so many of us had waited long years for, we got a joke-filled bit of nonsense. Now, I would say it could be used as a side trek for an extended, "real" Castle Greyhawk campaign, along the lines of how there were entrances into a Wonderland or Barsoom world from Gary's Castle Greyhawk. But that doesn't take away that TSR's "Castle Greyhawk" is one of the biggest disappointments in gaming.
I'll pile on The Forest Oracle, too. Poor writing is what did it for me.
Egg of the Phoenix is a module that irritated me. It simply doesn't hang together well, and the seams show badly where a number of modules were crammed together. Stuff like that works occasionally - the GDQ modules being the best example - but it failed badly in this instance.
Modules C3 (The Lost Island of Castanamir), C4 (To Find a King), and C5 (The Bane of Llywelyn) left a bad taste because they were simply lackluster. They came at the tail end of the classic era of modules, and were the first ones I recall not wanting to run at all. Plus C3 introduced the term "gingwatzim," for which I can never forgive it.