The "darkness" was excellent. Good Archer development. I like Archer best when he is making dubious ethical choices in Season 3, suddenly he's very interesting. The contrast from the upstanding and idealistic explorer in the first two seasons is great stuff.. and I think in season 4 we see an evolved Archer.
I do really like the contrast between Archer in Season 3 and Archer in Season 4. Home made a great point of this, but the entire season it was like we saw a much greater developed character and it was great. Pity some of the other characters (Reed) didn't get the same kind of treatment.