Forge of Fury is a classic - with the Roper, a CR 10 for a third level party?
Well, there you go!
Well, using 3.5 rules it actually became a CR12 monster
My group didn't have any problems with that encounter. I made it sufficiently clear that the roper was beyond their abiliies, so they wisely decided to negotiate:
In exchange for providing it with the corpses of slain enemies (food!) it released the party member it had grabbed and used as a hostage.
I remember only one classic adventure that we successfully wrecked:
It was "Tor der Welten" (~ Portal of Worlds) for the "Das Schwarze Auge" rpg (The Dark Eye):
The adventure is conveniently front-loaded with (magical) treasure, most of it being consumables, intended to be used up in the second, main part of the adventure, set in a different 'world'.
Basically, the adventure assumed that the party would be trapped at some point in the entry dungeon leaving them no other escape route than the title-giving portal to another world.
Naturally, our group was savvy enough to avoid falling into that trap (particularly after seeing the adventure's title) and simply left the dungeon with a full complement of magical treasure that served us well in our future adventures.