Similar vibe

Atmosphere is so important for a Horror film. Those three you mentioned all have fantastic atmosphere. It's no surprise they're all from the 1970s. The Sentinel (1977) is a bit different but is another that always comes to mind when I think of a strong, unsettling horror atmosphere.

It takes the basic plot & tone of “The Lost Continent” (1968) and combines it with the creative ‘Death Corps’ element. There are also bits from “Let’s Scare Jessica to Death” (1971), “Haunts of the Very Rich” (1972) and “Children Shouldn't Play with Dead Things” (1972), not to mention similarities to the contemporaneous “Empire of the Ants.”

There's a good eerie air that morphs into ghastly reality. The 70's atmosphere and cast are highlights, as is the spooky electronic score. Brooke Adams as Rose has an exquisitely sculptured face, but is otherwise fairly un-curvy.

The skeletal Cushing in his post-Hammer years is a professional and performs well. It takes years of training and practice to be able to play such a character with the corresponding ominous lines without giggling.

The set-up is entertaining enough, but the second half unfortunately devolves into redundant scenes on the island (zombies rising from the water and people fleeing in the woods or bog). While there are minor shock waves at the beginning, it’s a misnomer.

So, while “Shock Waves” is worth checking out, I’ll take “The Lost Continent” and “Humongous” (1982) over it. They’re both all-around more entertaining for this type of fare.