I found this film through TOERIFC (The Oldest Established Really Important Film Club) and located a way to easily watch it online at Movielab.tv.
Roger Ebert has a negative review. Senses of Cinema calls it a disaster. The New York Times closes its review with this:
Mostly, "The Serpent's Egg" is a movie of beautifully photographed weather and handsome period sets and costumes that encase characters who remain as anonymous as the bodies in a morgue. It's dead.
DVDTalk praises Carradine but generally gives a negative review ending with this faint praise:
...the picture is a beauty to watch and yet another unique curiosity. The best praise for The Serpent's Egg is that it creates a grim little genre all its own, Politico-Film History-Paranoia.
Only the Cinema opens with this: "To the extent that Ingmar Bergman's The Serpent's Egg has a reputation at all, it is not a good one."