Is it unusual to not have "good" dreams?

As long as I can remember, I've had nightmares and lots of 'em. When I was a kid, I dreamt about monsters and demons. When I was a teenager, I was killed more ways than you can imagine. Now, as an adult, the recurring theme is watching helplessly as harm is done to my loved ones, even including pets (who are like my children to me). I can count the number of "good" dreams I've had throughout my life on one hand. Is this common? If not, why do you think this is happening and should I consider it important?