I’m going to go against the grain and say that while I enjoyed Firefly, I also recognize its weaknesses in both the writing and acting aspects and can respect the o.p.'s negative opinions. The biggest strengths of Firefly is the often excellent cinematography and CGI effects, which are first rate, and its counter-genre sensibility. Instead of trying to resolve issues via the Particle of the Week method so popular on the various Star Trek franchises, it actually forces the characters to make hard choices and sacrifices. It also effectively integrated both elements of comedic relief and dark drama into the on-going storyline, and was clearly building a universe that was anything but a pleasant utopia in which only bad things happened outside the Alliance.
The writing, however, was uneven at its best. The stories were often highly contrived (is it really cheaper to ship live cattle from one moon to another?) and the dialogue could often descend to about an eighth-grade level. It didn’t help that when spoken by some of the cast–Morena Baccarina and Ron Glass in particular–it seemed especially stilted. Even from the naturally charismatic Nathan Fillion it was often somewhat awkward. Steven Baldwin as Jayne was awesome in just pure venal self-interest though, and Christina Hendricks’ couple of guest roles serve to highlight her talent beyond her gyroscopic abilities.
However, the really great moments–as when Mal, upon attempting to give back their money and release the henchman of their patron, is threatened with eventual death as a precursor to a future conflict, only to dispatch his would-be hunter into the port-side engine intake–really do set it aside from any other science fiction show. It implicitly acknowledges many of the absurd conventions of science fiction by lampshading them, as when Wash argues that telepathy isn’t real because that would be “like science fiction,” and then is bemused when reminded that they’re living on a space ship.
Firefly was basically a better show than anyone had right to expect it to be, but not the greatest show ever made by a far stretch. If you don’t like it, and it’s particular humor doesn’t ring for you in the first couple of episodes (which are actually some of the strongest, in addition to “Our Mrs. Reynolds” and “Out Of Gas”) then it probably just isn’t your cup of tea.