So, I just watched Darker than Black, season 2. I was hoping for it to be a bit more like the first season, but I really liked the ending. Sure, it wasn't dark (though it had it's moments), but I really liked the ending. I can't say it was entirely unpredictable (though I didn't guess a bunch of it, it wouldn't be that hard if you payed attention to certain details), but I felt that that was exactly where it had to go.
Considering that they brought in a character like Suou, and relied on emotions more than the original, and had many more light hearted moments and other crap (like using the word loli), it turned out rather well.
Overall, I really enjoyed it, I just kinda wish it had been a bit darker (no pun intended :/) than it was.