Just because a movie bombs at the box office, that doesn't make it a bad movie. It could just mean that its budget was too bloated to reasonably expect to fill the money pit back up, or the marketing was lacklustre, or the competition was incredibly stiff on opening weekend.
Or yes, maybe it was also a bad movie. Because sometimes the numbers are simply indicative of audiences saying "Thanks, but no thanks, that film appears to be garbage and I'd rather buy a couple of beers at the pub than watch your expensive garbage."
Still, tucked away beneath all the rightful flops like Gigli and Battlefield Earth is a small collection of movies that, while they didn't make any money for the studio, should be able to enjoy much better reputations. They may not have been great financial successes, but they're actually pretty solid, engrossing movies if you don't let yourself get scared off by the negative box office numbers.
Most of these are likely doomed to remain inextricably tied to their overall gross, but maybe you could give them a second chance?