Sure, the plot devices are often a little silly and convoluted, with each kill or attempted kill being crazier than the last, but Price (whose dialogue is delivered entirely via looping) is in fine form, the dialogue -- particularly from the detectives -- is clever and often very funny, the characters are entertaining and the set design and costumes are often quite breathtaking. (And all done on a budget of $500,000!) The ending felt a bit abrupt, but I'm sure they were leaving room for a sequel.
I'd imagine this colorful Corman type brand of '60s horror was starting to become old hat by 1971, but this is certainly a strong entry. This had to have been influential, as it brought to mind shades of later films...Phantom of the Paradise first and foremost.
Also, the delightful Terry-Thomas was woefully underused here.