In Escape From Tenh (COR2-11) Ethercreatures (wierd bugs, including variant umber hulks) rampaged out of nowhere to decimate the Duchy of Tenh (already in bad shape from Iuz and Stonefists)
They ate everything in their path, and they spit stuff at you that made pieces of you vanish on to the ethereal plane. You had to escape from Tenh in the adventure where the ethercreatures arrived.
Then you went back in Into the Dying Lands (COR2-13) to do some reconnoitering, and help a guy who lost someone, IIRC. You might have seen a 'ropey' looking leader type off in a distance if you were lucky.
In Isle of Woe (core special), the The Isles of Woe resurfaced, and it was revealed that the caretakers of the Isles let the ethers out ages ago, and they had knowledge of how to put them back. the Codex of the Infinite Planes was involved.
In Dust of a Dead World (core special), you could also travel to another world that had been wiped out by the ethers, except for some thri-kreen who held on tenaciously. There you could attack an ethergaunt leader if you were playing high-level. They tended to be pushovers.
In Return to the Isles (COR3-02), you went into a secret chamber in the Isles and recovered a sword and hands of Yagrax, which would direct you to Yagrax's tomb.
In Sepulcher of the Wizard King (COR3-10) You went to Yagrax's tomb to recover the lost spirit of Yagrax, who could successfully use the codex (anyone else would become insane) to banish the ethers. Yagrax's tomb was guarded by metal people who used to live on the isle of woe and now were metal people.
In Endgame (COR3-12) Yagrax took over an NPC and lead you through different planar realms until you got to a place where you coult let Yagrax banish the ethers using the codex. Then Iuz' forces show up and take the codex away. (a bit railroady?)
I thought it was a good bit of fun. Combat intensive. The ethers were interesting. The ethergauts tended to be pushovers. The Isle of Woe scenario was released as a home play megasceario and was alot of fun.
Controversies: the plots were a bit railroady. But not all.
The ethers were supposed to be a flanaess-spanning threat and I belive that some regional traids resigned rather than put up with forcing ether threats into regional scenarios.
I continue to wonder if it was a reconfiguring of the plotlines Erik Mona had been working on in LG with the Lost City of Darkash Anam, which is supposed to have a tower inhabited by insectoids. His plots seem to have been abandoned, though my PCs carry along certed books from his scenarios.
Echo (COR2-08) was related but not an actual part of the series. I think some deleted text from that mod (in the copy I got anyway) implied that the destruction of the Zochal freed the ether creatures from their prison. Echo was widely regarded as a bad trend in LG, as Stephen Radney McFarland took over at that point, the mod seemed to be based on the ideas from Sonic the Hedgehog (you leaped on platforms in varying elemental environment), and you could lose your PC for no apparent reason. SRM was also credited with making LG do away with 'roleplaying' xp and telling players that D&D expected them to min-max, and that profession and craft skills were expected to be useless.