In fact, I've seen worse acting in major studio productions, even worse dialogue. The one thing that is definitive about this film is the effort and commitment put in by cast and crew. Kenzie Phillips has genuine screen presence while all the rest of the actors give it their best but aren't as convincing in their character portrayals. There is some dialogue that is misplaced, but most of it works and serves its purpose fine; the camera shots almost seem to get better once the action gets moving into the horror scenes, as before that much of the character-building feels standard film shooting; some humorous moments, not so much in the jokes or quips, but with special effects being overdone on purpose and splattering the characters.
The actual horror element beyond the gore and monster mutations is surprisingly well done, but it doesn't arrive until very near the end; the rest is a slow build-up but when the gore kicks in, it really kicks in!
I don't think you'll miss anything by not watching this film, but the next time you sit through a 2hr40m major Hollywood production that seems interminably boring, long-winded, and actors are just phoning in their performances, remember there are some films out there that offer simple 1hr30m enjoyment with far more conviction and genuine love towards what is being produced. It doesn't take huge budgets to make good films - just passion and commitment.