Joss Whedon is a genius. We know him better by his popular serials like Buffy the Vampire slayer and Angel but my favorite of his works is TV series Firefly.
Firefly first aired on FOX in 2002 (US) and was canceled after fourteen episodes (three of those were not even aired). i watched the entire series on hulu.com (which is an awesome site btw :)). Low ratings were cited as the reason for cancellation of the show. The show always had a dedicated lot of fans but that could not bring the show back (a la Family Guy).
Firefly is my TV's Star Wars. It is just awesome. The series has a very different genre... not the typical aliens and inter galactic wars and time travel stuff but of a mix of future civilization and western settings. The series takes place in 2517 on several locations (planets, moons, spaceships). As time passed by on Earth, humans used all the resources and moved out of Earth and colonized many other planets in a different star system. Many of those were terraformed, a process in which a planet or moon is altered to resemble Earth. The process made the planet habitable but did not make it high tech. Which meant some of them (mostly part of 'alliance', a large consortium kind of planets) were very developed and while some planets were just habitable making them resemblance the wild west :)

The title of the show comes from the class of the space ship (called Serenity), which features all the main characters of the show, called Firefly (it looks like one with tail lighting up during acceleration). The awesome mix of the western genre and sci fi takes the series to a cult status.
Like all great TV series, Firefly had a great ensemble cast. Malcolm Reynolds is the captain of the ship Serenity and took part in so called Unification War (War between Alliance and other independent planets, Alliance wants to control those 'uncivilized ' planets). Zoe is second in command on serenity and she served under Malcolm in the war. Washburne is the pilot of the ship and husband of Zoe. There are several other characters like Inara the companion, Janye the soldier, Kaylee the sweet mechanic ;-), Simon the doctor and river his genius sister and Book the shepard.
Firefly takes place in a multi-cultural future, primarily a fusion of Occidental and Chinese cultures, where there is a significant division between the rich and poor. As a result of the Sino-American Alliance,Mandarin Chinese is a common second language; it is used in advertisements, and characters in the show frequently use Chinese words and curses.
The writing of the show is crisp and intelligent. The episode were aired as one hour episodes. But unfortunately after the end of 14 episodes the viewer is left with lots of unanswered questions (unlike Studio 60 on the sunset strip which was also canceled after one season ). Many of the questions were answered in the movie Serenity which is continuity of the TV series. I haven't seen the movie but the movie has got critical acclaim and already has a cult status like the series.
All in all, this series is great mix of drama and action. A Must watch!