Kudos to Robb White [House on Haunted Hill, Thirteen Ghosts] for an intelligent script that is well thought out with great dialogue and suspenseful moments. Castle took this wonderful script and ran with it full force. I think it's one of his finest films and proves he was more than a just a gimmicky filmmaker. I've always been a big fan of his work and this one cements my admiration for him all the more.
Homicidal also includes some great acting. Joan Marshall is fantastic as blonde bombshell Emily. She has a long list of TV credits to her name and totally nails this character. It's overly-dramatic in all the right places and a bit "going off the rails on a crazy train" when it needs to be. The other women in the cast are really strong as well. Eugenie Leontovich is fun to watch as the wheel-chair bound, mute Helga Swenson, the matriarch of the family. She has a slightly creepy look with big expressive eyes that serve her well in this role. The rest of the cast also deliver veyr good performances as well.
The icing on the cake is Hugo Friedhofer's score [Casablance, Midred Pierce] which heightens the tension of every scene. Furthermore, Burnett Guffey's cinematography [From here to Eternity, All the King's Men] is great with many scenes illuminated to perfection to maximize the tension.
Have fun with this one. It's not quite Psycho but they are next door neighbors in terms of quality of storytelling and visual impact. Enjoy!
For more info check out the film's entry in IMDB.