Season 1 was great although a bit over-rated (I don't mean that as a knock on the season in any way, it simply did far better than it should've at the emmys, although oddly enough, the best actor on the show was the one who didn't get nominated
). Season 2 was disappointing and pretty uneven (if season 1 was the Trinity Killer Season of Dexter than this was the season with that random religious nut + Tom Hank's son). Season 3 was basically a really, really bad season of 24, but without Kiefer Sutherland's consistently excellent performance (disclaimer, I quit watching mid-way through season three). I would only recommend season 1 and would argue it would've been better if they just made the first season a miniseries or something.
