Teenagers from Outer Space (1959)

How bad is it? It's one of the worst 1950's sci-fi films.
Should you see it? Yes.

A young alien falls in love with an Earth girl and ruins the plans of the invading aliens, who are equipped with (toy) ray guns and giant lobsters they raise for food. The teenagers are all played by actors too old for the parts, the costumes are laughable, the acting is poor, the sound isn't properly synced and the monsters are seen only in shadows and superimposed. Mostly, though, it's the dialogue that generates laughs. Supposedly budgeted at $20000, as has been said elsewhere, little of the money shows up on screen.