Hard show to rate. Seasons 1 and 2 are a mixed bag - both have quite a few really good episodes, but also a lot of crap that made me wish I had been watching almost anything else. Season 3 is fantastic, especially the final few episodes - it's like it's a totally different show from the first 2 seasons. Season 4 feels like a different show again, but not in a very good way. I liked how season 4 had a narrative stretched over the whole season rather being so episodic like seasons 1 and 2 were, but the plot feels as though it's stretched on for more episodes than it needed to be, plus it feels very Americanised compared to the seasons that came before.

My average rating for the 4 seasons works out as 6.75/10, but I'm inclined to round down to 6, simply because I felt as though season 3 was more of an anomaly than anything.