Carl Laemmle wasn’t a horror fan, so the early 30s horror cycle at Universal was more the work of Carl Jr. When the studio was bought in 1936, the new owners weren’t horror fans either and killed the films off. But the unexpected hit revival of Dracula and Frankenstein in 1938 made them, like uncle Carl, realise you didn’t have to approve of your product to make money from it. And so, with Son of Frankenstein, the cycle began again. Son has some terrific set design (dig the shadows from that staircase), it’s quite well acted and was evidently conceived as a big film… but it’s not the same somehow. I find it a bit hard to believe that no one seems to connect the deaths of all the jurors who sentenced Ygor to death with Ygor himself, but the film’s most problematic aspect is its recasting of the creature as, well, the monster it was always described as. It’s Ygor’s tool rather than the independent being it was in the first two films; it’s been downgraded by the people who took over the horror films under the new regime from those (especially James Whale) who owned them before. And, alas, the films themselves would soon suffer a similar fate. Karloff was wise to give the character up after this film.
One other thing. I’m puzzled by a few things in Bill Everson’s book on horror films, but more so than usual over a claim he makes about this film: since teeth-grinding little Donnie Dunagan isn’t afraid of the monster, the film makes it impossible for the audience to fear him (the monster, not the child). Curious that he doesn’t lay the same charge at the feet of the first film, in which another child famously isn’t afraid of the creature. Maybe Everson was just disappointed the child didn’t get killed this time around.