Now, I'm not going to pretend I'm some SciFi expert by any means; I started watching this show on the recommendation of a friend of mine, but I've gotta say I have thoroughly enjoyed Firefly.
To set the stage, there was this intergalactic war between The Alliance and, I dunno, The Rebels or something. Just think of it this way: The Alliance = Darth Vader, The Rebels = Luke Skywalker + Prostitutes. Oh, but if only it were that simple. See, in this time and place, The Rebels lose the war and are forced to abide by Alliance rule. This doesn't sit too well with Malcom Reynolds, captain of the firefly ship 'Serenity'. See, Mal was a sergeant in the war against the Alliance, so as a final Fuck You to authority, he buys a firefly, compiles a crew with his second-in-command from the war, Zoe, and together they go about making a living any way they can. This involves illegal smuggling, outright thievery, and any other means they can take advantage of to make an ends.
The crew includes the comic relief, firefly pilot Wash; the brute thug Jayne (yes, a girl's name on a male Baldwin brother); the super-cute firefly engine mechanic Kaylee who's got a crush on the doctor, Simon; the doctor's sister, River, who's brain is scrambled due to illicit Alliance testing; the shepherd, a priest of sorts who knows a lot about things he probably shouldn't; and Inara, the sultry seductress who works as a legitimate prostitute in this glorious fantasy land where whores are revered, as they should be!
Together, they go galavanting off on adventure after hour-long adventure. Some have dubbed it the first Space Western, where many old west themes are interspersed with the high-tech life of space travel. It was created by Joss Whedon, the same guy who brought you Buffy The Vampire Slayer, so the writing is top-notch and the characters are well-crafted. Unfortunately, this is yet another one of those shows where it has a hardcore fanbase, but was lacking in overall ratings. I'm assuming it was also pretty expensive to keep around, since no other network deemed it worthy of taking on once Fox gave it the ax. Those ensemble casts with quality writers will do that to a good show. It lasted not-even one full season, then was given a feature-length movie as a coda a few years later (which I still have yet to see, but Netflix says it's on its way).
My thoughts: if you're into SciFi, you'll most likely dig this show. Even if you're a noob like me, though, I'd give Firefly first crack at your SciFi Cherry. Obviously, Science Fiction - like any genre - can be hit or miss when you figure in the varying standards of other series, but Firefly was a genuine hit that deserved better than it got.