How bad is it? It's a minor monster movie, done poorly.
Should you see it? It's just barely watchable.
Prehistoric monsters covered with slime climb out of the sewer to create a dome over the city of Los Angeles, as part of a plan to lower the temperature aand support the growth of fungus. The first few minutes are the best. Tom Laughlin, who later did the "Billy Jack" series, makes an early appearance. There's one great line: in a romantic situation, you hear "When I'm with you, I don't even think about slime people."