I've seen all the Firefly episodes and the movie more than once and like many I loved them. I think Joss Whedon's secret recipe for success in all his endeavors has always been his ability to create particularly endearing characters who perfectly populate the scripts he works with. This was perhaps especially true of Firefly.
Whedon's problem is that he has forgotten how to put in a well-balanced cast of characters. Yeah, Firefly was great. But you're just not going to appeal to a wide audience when all of the main cast members are basically Han Solo. You can only have one.
It's also why Dollhouse failed too. You've got an entire cast of individuals who fall into one of two categories. Victims who get their personalities erased and are sometimes rented out to high-paying clients as actual mindless sex slaves. Or ... Those who work at the dollhouse, know what's going on, don't do anything to put an end to it, and are basically immoral jerks that the audience couldn't care less about. When the rumors started that Alpha was going to launch an attack on the dollhouse in an upcoming episode, I cheered! Most of the fans probably did. Finally, someone capable of taking down the dollhouse and freeing the "slaves." And then it turned out that Alpha was a psychopath who was infused with multiple personalities all at once. Except for his own, which he deleted forever. Nice ... Give the fans one character that they can actually get behind, and then pull the rug out from under us by making him a deranged lunatic with incredible combat skills who likes to slash the "dolls" (both male and female) across the face multiple times. So basically, just another jerk. Then it turns out that the last character the fans could get behind, the detective, decided to sell out completely to save one of the "dolls." He barely even tried to put a stop to the dollhouse.
Ironically, Whedon is probably still wondering why Dollhouse got cancelled. Well, when every single character with free will turns out to be an absolute jerk or just easily quits, and then you toss out an episode where you make it blatantly clear that the dolls have no escape whatsoever ... Yeah, no one's going to care about your show. Buffy had a balanced cast, so did Angel. They both had successful runs.