Sevigny, who stars as Nicolette Grant in the HBO drama, explained that the show became too "far-fetched".
In an interview with The AV Club, she said: "It was awful this season, as far as I'm concerned. I'm not allowed to say that!"
She continued: "It was very telenovela. I feel like it kind of got away from itself. The whole political campaign seemed to me very far-fetched. I mean, I love the show, I love my character, I love the writing, but I felt like they were really pushing it this last season.
"And I think with nine episodes they were just squishing too much in. HBO only gave us nine Sundays, because they have so much other original programming - especially with The Pacific - and they only have a certain amount of Sundays per year, so we only got nine Sundays. I think that they had more story than episodes. I think that's what happened."
Sevigny also revealed that the cast members only receive scripts an episode at a time, explaining: "We never know what's going to happen in the next episode until we're almost finished shooting the one we're shooting at present. Me and the girls [Jeanne Tripplehorn and Ginnifer Goodwin] definitely were not very happy with where it was going - or more like, 'We really hope it's going to work. It seems like they're really pushing it'."
Asked about the storyline in which JJ tries to inject Nicolette with an incestuous baby, Sevigny replied: "Oh God, I know. Oh God. It's too much. It's too much.
"But I hope the fans will stick with us and tune in next year. There's a lot of people who really love this season, surprisingly. God, I'm going to get in so much trouble."
HBO ordered a fifth season of Big Love last month.