How bad is it? It's a terrible idea, poorly done.
Should you see it? Probably not.
Slugs aren't scary and this film does nothing to counter that fact, though there is a surprising amount of gore in this one. Spilled toxic waste gets eaten by slugs, which attack naked teenagers on Halloween - it's just that unoriginal. It's also badly dubbed. So how do slow-moving slugs kill? They have teeth, but the people tend to kill themselves off in fires and accidents. None of the characters are likeable, so you almost want them to get killed and eventually they manage to blow up the entire town.