It's not exactly a major shock that Boris Karloff plays a mad scientist in this film, though it is very unusual the way he plays this role. Instead of the evil twisted genius set on making monsters or ruling the world, Karloff's goals are incredibly noble. And, when he later kills, you really understand with and could possibly condone why he did this. The moral implications of the film are astounding! As for the rest of the film, the writing for this sort of B-movie is very good, the acting fine and production values work out well (proving you don't need a huge budget to make a good film). About the only negatives at all are the ending (I would have just ended the film a minute or two earlier without the unnecessary final scene) and a mistake in the film about how deep the lab was under the earth. In the beginning, they count 191 steps to the bottom of the shaft to the lab, but later, it's just a homemade ladder about 12 feet long. Regardless, it didn't harm the film in any serious way and the film is a very good 'mad scientist' flick that actually is good entertainment and well thought-out.