I recently watched this one for the first time with only the least understanding of why it generated so much stink in the 80's. I had a grimace on my face most of the time. The movie isn't scary in any way as I see it, it's unsettling.
The gore effects and animal mutilations alone would just have made it a shock movie but what drove it over the brink for me was that musical score. This was especially so with the turtle (I knew nothing about this scene prior to viewing!) and the dismemberment of the cameraman. They sure hit all the right negative mental notes with that music.