Difficult to say. It's not really similar to any other show except perhaps Buffy or Angel (which I haven't watched). For example one could compare B5 to DS9 as being similar shows but with Firefly you can't really do that. Overall I liked the show and thought the mythology and characters were well though-out but at times it was a bit too "cute" for my tastes. There's this kind of sarcastic self-aware quality to the writing that I was never entirely sold on.