Mr. DuLac’s review published on Letterboxd :
One doesn't easily forget, Herr Baron, an arm torn out by the roots.
I had never watched Son of Frankenstein because I figured it was just a cheap sequel and never looked into it further. This ended up being a huge surprise. It's not as ambitious as Bride of Frankenstein, but it's still a surprisingly excellent film that actually tells a great new story featuring Frankenstein's Monster and doesn't try to just copy the original or Bride.
The set designs, style and overall look of the movie continues the gothic surreal look of the last film. I would dare say that it might even pull off the sets even better, I know that's sacrilege but by no means am I saying it's a better film. I'm just glad that it seems none of the contractors in the town own any sort of level and are incapable of building anything that resembles something straight.
James Whale and Colin Clive aren't involved in this one, but to make up for the loss we get Bela Lugosi introducing the iconic character of Ygor (later spellings would be changed to Igor). The original Ygor is nothing like what the public perceives the character to be. Most people actually picture the hunchback Fritz from the first film. The original Ygor is no lab assistant and is in fact a central character of the story. It's also possibly Lugosi's greatest performance on film.
In the end you get a great original Frankenstein story that doesn't try to recreate the two previous films. Great set designs and production values. Two of the biggest horror icons, Karloff and Lugosi, in one film. A truly great and fun horror movie.