SOME SPOILERS CONTAINED WITHIN
Season 1 is ok. Season 2-3 are just epic, Scorpius owns the shit. His back story episode is one of my favorites, he's cool as a cucumber and always one step ahead. Season 4 is more or less trash, by far the worst season. Scorpius doesn't belong on the ship and it doesn't make much sense that he's there. And while the show was always wacky, the plot of the episodes were overall pretty weak. The new redhead chick is hot but her character ends up being dumb bullshit.
Even a lot of the mini series was pretty crap but it was still a lot better than season 4, plus it was a crime to drop the series where they did. I only watched season 4 because I was so pumped coming off of seasons 2 and 3. If I wasn't watching them rapid fire on DVD I probably wouldn't have made it through.
Anyway, I'm pretty sure Farscape was canceled mostly because it was expensive compared to Stargate SG1 which from the looks of it requires a handful of basic props to film. The show is also tough to pick up and make sense of from the middle, which is a problem with many scifi shows.