This early-70's proto-slasher is a pretty enjoyable fair, especially if 70's horror is your thing.
Occasionally a bit dry, I think, for the most part, The Severed Arm keeps the interest of the audience. The gore is certainly lacking (though there are a few fun scenes, especially one toward the end), so that's certainly not a reason to recommend the film. Still, the plot itself is decent, and I think anyone can see how it's not too dissimilar from many slashers past this point.
There were plenty of enjoyable actors and actresses throughout. The two main characters, played by Paul Carr (later in The Bat People and Sisters of Death) and David G. Cannon (this is his sole film) - both do a pretty good job, Carr reminding me of Gary Oldman at times. Deborah Walley has a decent presence, mostly toward the end of the film, as her interactions with Bob Guthrie (who was in only one other film) were pretty enjoyable. And who couldn't get a kick out of Marvin Kaplan (who appeared in the comedy classic It's a Mad Mad Mad Mad World from 1964) playing radio host Mad Man Marvin? His over-the-top hamminess provided most of the fun for this film.
Which is true mostly in part because, like most 70's horror movies, this film plays itself pretty straight. It even had a bit of a downer ending, which, given the sometimes television-feel this movie has, might take you by surprise. Still, despite the lack of solid gore, I still think anyone going to a drive-in to watch this probably got a kick out of it.
I liked The Severed Arm when I first saw it last year, and I still like it. The ridiculously lengthy flashback was good fun, and the final scenes really close this movie on a fun note. It's a solid proto-slasher with a moderately decent cast and story. Certainly a 70's movie worth looking into. 7.5/10 (rounded up to 8/10 to fit site's format).