The first Tales of the Jedi miniseries in 1993 was a proof of concept: Star Wars four thousand years early, with different ships and the same Force. Dark Lords of the Sith is the one that proves the concept was worth having.
Two falls, told properly
The book runs two descents in parallel and refuses to make either of them a single bad decision. Exar Kun is a Jedi with a scholar's curiosity and an enormous ego who goes looking for Sith holocrons because nobody will tell him what is in them; by the time he understands the bargain he has made, the bargain has already been made. Ulic Qel-Droma's fall is slower and sadder — he infiltrates the Krath as a deliberate, sanctioned operation, and the story is honest about the fact that a good plan executed by a proud man is still a trap.
What Veitch and Anderson get right is the institutional failure around them. The Jedi in this era are numerous, scattered and badly co-ordinated, and every character who could have stopped either man is somewhere else, sure that somebody senior is handling it.
Chris Gossett
Gossett draws five of the six issues and his figure work is the reason the era feels ancient rather than merely early — heavy robes, rough stone, lightsabers that read as artefacts rather than tools. Hugh Fleming's painted covers are the other half of the argument: they made a comic set four millennia before the films look like it belonged on the same shelf.
What it started
Exar Kun goes on to haunt Kevin J. Anderson's Jedi Academy novels, and the vocabulary invented here — Sith holocrons, Korriban, Massassi, a Sith Empire with an aristocracy — is still load-bearing in everything from Knights of the Old Republic to the 2022 animated shorts. Almost none of it is canon now. All of it is why the Old Republic exists as a setting at all.