Possibly part of the reason I couldn't totally buy into season 4's premise is that, for me, John Lithgow will always be the hilarious High Commander of Joseph Gordon-Levitt and co. Great actor, great performance, but that's the trouble with playing a role for a long time - viewers can find it hard to accept you as a very different character.
I don't know how popular Third Rock From The Sun was, maybe I'm the only fan around here.
Mild spoilers for anyone who hasn't seen up to the first episode of season 2.
Spoiler
I thought the second season presented a more interesting situation, with Dexter pursued by his friends and family (the good guys, as opposed to the usual menagerie of scumbags), and facing a couple of ridiculously difficult moral dilemmas. I also loved that it continued stories from the previous season, with Dexter coming to terms with himself after effectively looking in the mirror, and Debra becoming increasingly scarred in the aftermath of a traumatic ordeal. This last season's been the only one that picked up strands of the previous year so strongly.