I'm going with a 4 as well - would have been 4 and half if possible.
Like Saber, I much preferred the female Eldrad - the male one was, for want of a better word, naff. She was believable as a malevolent character, whereas him I just didn't buy at all. Really let down the last episode. As did the way he 'tripped' over the scarf - I'm sure that could have been a bit more convincing.
Some of the characters at the power plant irritated me a little, at least at first. This may be to do with how acting has changed over the years though as initially they seemed a little over acted (yes Watson & Miss Jackson I'm looking at you) - once I got past that/used to it they were fine.
I loved both TB & LS though, and the ending was really well done. The story moved at a nice pace for the most part & up until they moved to Kastria, Eldrad was an interesting character (although maybe a bit of mystery about his/her true motives
would have been nice).
All in all a good solid story