While the movie got negative reviews at the time of release, I would argue it's much better than the people who reviewed it at the time thought it was.
For one, it's Shown Their Work The Movie. Many facets of the movie display a profound knowledge of the source, done quite well in live action format, complete with the dinosaur power technology, the characters are dead ringer for their cartoon inspirations, and all the series specific touches are given some attention.
Second, it's got a plot that could have easily been done in cartoon format with a few minor changes and fit perfectly in the series continuity.
And finally, it's not the kind of movie that would set the world on fire, but it captures the heart and soul of the Flintstones in live action format, and as someone who enjoyed the cartoon, I'd recommend it to fans if they need more Flintstones after marathoning the cartoon.