Blake is certainly the character the writers spent more time creating a background for, and we also have seen many of his reactions to events around him. All that makes him a character we can relate to and care about. As the most fleshed out person in the story so far, he seems much more real than everyone else. Avon is potentially good, but could slip into cliché territory very easily as the "Han Solo cynic" type. Now taht I know he's going to be around a while longer, I figure when the writers came up with the character they didn't really understand the impact Avon was going to have on the show. The one that needs developing the most is the lady, Stannis, if I recall correctly, because she doesn't seem much more than pretty with great hair, and one who won't trade sex for favors (but then she doesn't seem desperate at all to resort to that yet).
The pace is very "British," which reminds me that the notion we had of European and American productions back in the 1970s: European stuff is more artsy, more boring, with longer scenes. American shows and movies favor more action, are more superficial and, in general, more standardized in terms of cinematic language. The interesting things about this all is that even if that was true or partially true once, it no longer makes a difference, since now European productions are as dynamic as the American ones, and American shows can be equally "artsy" if that's what you're looking for. Anyway, in 1978 a show like Blake's 7 was easier to identify as British.
The dramatic set up is good. The situation is simple enough for us to know who to root for, but complex enough for the story to develop into unforeseen consequences. However there's a still a major problem: there's no clear antagonist. A faceless tyrannical government doesn't qualify as such.
It just occurred to me that the characters are potentially compelling, but in the beginning you see a bunch of White English people and they all have more in common than differences. Nowadays you'd have people of different ethnicities, which would make them different from the very beginning. But in shows from the past that was not the case. However, in Star Trek, you also had a bunch of White guys, but they were distinct enough from the get-go. You had young and handsome Captain Kirk, Spock (the resident alien), McCoy (not known for his physicality and with a more noticeable Southern accent), Sulu (an Asian), Uhura (a Black woman), Scottie (another one with a different accent), Chekov (again, accent and somebody younger than the rest). Each character is easy to identify and remember for certain characteristics. In Blake's 7 I'm still trying to get used to who is who, except for Blake. OK, there's a woman, obviously (great hair!), Blake (even greater hair!!), and Avon (OK hair). But that Villa guy, I don't remember what he looks or sounds like.
If I were watching this by myself, I might have continued or not. I'm not totally buying the show yet, but I'm reasonably interested.