Although Hammer specialised in reinvigorating older horror film traditions (Frankenstein, Dracula) they also had a number of opportunities to start their own - their radical reworking of the Werewolf story, for example, or 'The Gorgon', both of which could have easily have been turned into a franchise.
'The Reptile' has a great premise: a group of Burmese snake worshippers have the ability to transform their people into cold blood, skin shedding monsters (who then come back to England to live in Cornwall). With a less rushed, more considered script, and perhaps Peter Cushing to tell the the back story and give it credibility, it could have run and run.
As it is, we're left with a decent Hammer film with a singular storyline that incorporates a very odd monster, a lot of green, drooling faces, Private Fraser from 'Dad's Army' and a sitar jam that ends with an autodestructive finale straight out of a Who concert.
The narrative is nippy but slightly repetitive (see 'green, drooling faces'), and the whole film cries out for a strong lead, although dear old Michael Ripper does his best in a fair sized supporting role and Jacqueline 'Servalan out of Blake's Seven' Pearce is an attractive female presence (some of the time).
Something of a missed opportunity, but generally good stuff.