Somewhat Unfinished
The Abominable Dr. Phibes shows signs of being rushed, or underdeveloped, its sequel even more so. The storyline shows such promise, and is certainly the ancestor of serial killer films such as Se7en and Saw. (The latter even employs the key imbedded in a living victim, originally imported from Phibes.) The decision in Se7en to utilize fewer murders (seven deadly sins vs ten plagues) is a wise one, since it leaves Se7en more time for character development, one of the weaknesses of Phibes.
A camp sensibility informs The Abominable Dr. Phibes, with the music, showtunes, Beardsley-esque decor, costumes, and the presence of the voluptuous Vulnavia ( in whom Phibes has no interest whatsoever); his devotion to his wife Victoria notwithstanding, Phibes is one of the gayest characters Price ever played. Both Phibes films end with a rendition of "Somewhere Over the Rainbow," an unusual use of the tune that makes us feel further empathy for the tragic Dr. Phibes, monster though he seems to be.
The audience takes a fiendish delight in anticipating the fates of the victims, though it would have helped if we had been made to feel that they deserved it more. Terry-Thomas in particular takes delight in his role, tippling copiously and leering with relish at his Victorian equivalent of a porno film. Oddly, this makes us have more empathy with his character; one regrets his death more than that of the others, and for that, his exsanguination seems somewhat more compassionately and painlessly executed than the others. What Dr. Longstreet may have done to deserve this mercy, we are not informed.
The policemen investigating the murders develop into comic relief. It's possible the studio was modeling them on the success of another film series begun by A Shot in the Dark, whose investigator so completely took over the film series that in time, audiences forgot that the 'Pink Panther' was originally a coveted diamond in a suspense film originally intended to be about a celebrated thief (Arsene Lupin, anyone?) The police investigators in Phibes show evidence of possibly having been seasoned by producers in this way, hoping to add to the film's appeal with audiences.
The character of the one victim-to-be who is given a role in tracking down Dr. Phibes, Dr. Vesalius (Joseph Cotten) undergoes a transformation from an eccentric deeply absorbed in his model trains to the man possibly capable of stopping Phibes. The name his character is given, Vesalius, was probably intended to be based on Dr. Hesselius, a recurring character in J. Sheridan LeFanu's stories. Hesselius is employed as a sort of metaphyisical expert in those stories, something of an antecedent to the Dr. Van Helsing of all the stories based on Stoker's Dracula. It's probable that Vesalius was intended to be an adversary of Phibes, more his equal than a hapless victim, but that this notion was never fully realized. It might explain Vesalius's easy recognition of Phibes's pattern, the G'tach (then again, he might just be Jewish). Having said what I've said about Vesalius, however, I'm rather glad that he was never developed into an arch adversary; it would have stood in the way of Phibes becoming an antihero of sorts in the second film. The second film completely refashions the character of Phibes from a madman bent solely on vengeance to a deeply maligned man with a definite positive goal, i.e. eternal life with his deceased wife Victoria in Elysia. We (the audience) are definitely meant to see Phibes as more deserving of attaining this goal than his adversary, the dislikeable Robert Quarry. Phibes's pronunciation of his assistant's name changes, from Vul-nah-via in the original, to Vul-nay-via in the sequel.
These sorts of inconsistencies in the storyline is likely a result of too many cooks spoiling the broth, together with a general rush to completion. One might wish to see Dr. Phibes redone, if only Vincent Price were still around to play him. He is irreplaceable.
...they seem to know where they are going, the ones who walk away from Omelas.