I think some of the criticism here is very undeserved. Take the effects in the old Flash Gordon serials or the original KING KONG....sure, they look positively primitive now, but you have to consider that they were cutting edge at the time they were released.
I would define bad special effects as something that doesn't fulfill what today's technology affords it (such as the horrendous CGI effects on most of the SyFy Channel movies).
Or my all time favorite bad movie, JAWS THE REVENGE...was it just me or did the shark look more and more fake with each film in the series?
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"The nine most terrifying words in the English language are, 'I'm from the government and I'm here to help.' - Ronald Reagan