Yes this is a regional movie filled with actors who either weren't actors or did small theatre work. Yes this seems like a movie made in the late 1960's not in 1977. And yes the title doesn't have anything to do with the movie which is more like Richard Speck than "Son of Sam." Finally it's an exploitation movie with almost no real exploitation, there is no nudity at all and the violence that occasionally happens is done so poorly it doesn't have much of any impact.
Having said all that the basic idea is solid and a bit unusual, the killer is trapped in the building early on with police sneaking in to try to find him. The killer is mostly only seen in bits and pieces--wearing kind of goofy brown loafer shoes. But the use of shadowy eye and eyebrows moving amid shadows while an electric tone/music drones on is rather novel and occasionally effective. Also the movie uses freeze frames to end scenes rather frequently rather than dissolving of cutting away. Also a few of the murder scenes come when you don't expect them. And the movie moves along pretty well, or well enough that you don't have to fast forward--if you don't just stop watching because of the cheapo production and acting.
These odd elements and the general crudity of the production gives it some grit. The budget is so low--they don't seem to be able to really purchase or rent even one really convincing police uniform, let alone the motely mismatched SWAT uniforms on display.
It also has and probably always had, sort of poor lab work with flat lighting and, now, faded and shifting colors, but this too now is seen as part of a Grindhouse Esthetic--in that way time has been kind to this movie.
It may be barely a movie but it tries, if doesn't succeed, at some style and has a few surprises, so can't say it's totally worthless, especially for those who will watch something that lacks the easy slickness of Hollywood films that can have no real ideas to offer.
