Slave Pits of the Undercity (1980): Both covers are by Jeff Dee. On the front, the wizard’s light spell saves the viewer and the party from utter darkness. (His non-casting hand is awkwardly placed, no?) Somehow, I don’t think the giant ant man’s two wooden shields are going to hold up against that hammer, but we have no idea how many of his friends are skittering to his aid, and that builds suspense.
I suspect the back cover was a rush job. The figures are finished (I like the bandaged arm of the bad guy), but the background is a blank.
Secret of the Slavers Stockade (1981): Jim Roslof did the front cover. The torch light and ensuing shadows set the mood, but the scene doesn’t sell the threat: the slaver and his Gollum-like pet are no match for the waiting heroes. The back cover is Erol Otus. The man is in absolute command of color and light, and his figures are the stuff of myth, something you might see on the vases and holy artifacts of an ancient civilization.
Assault on the Aerie of the Slave Lords (1981): Front cover is Jeff Dee again—substandard work, in my opinion: no motion, no life. The back cover, another Otus, is exactly the opposite: I can feel the pillars shaking, hear the cries of the warriors, the swooshing of the torch.
In the Dungeons of the Slave Lords (1981): This cover, one of Otus’s best, is a phantasmagoric, fantasy-art-meets-German-Expressionism masterpiece. It belongs in a museum. Bill Willingham goes for the throat on the lurid and bawdy back cover, a nice homage to Hammer Horror.
All of the modules (A1 – A4) were collected as Scourge of the Slave Lords in 1986. The cover painting here, a decent Frazetta emulation, is by Jeff Easley. (Is that Thundarr bursting his bonds in the background?)
Unfortunately, the series is not yet available on dndclassics.com.