Here in the Netherlands British television prior to cable/satellite television with the BBC we did get Dr Who on public broadcast, but Blake's 7 only 2 seasons and it was never repeated, and that was before my time. Therefor it wasn't part of our cultural memory like Dr Who. So when I heard about Blake's 7 I was very interested, first because I heard about it's premise (dark/dystopian/sarcastic), secondly there haven't been any good space opera's lately. I was a fan of Star Trek, but the quality drop under Kurtzman makes it unwatchable for me.
I really didn't mind the low budget SFX (even for it's time), I approached Blake's 7 like a theatre stage play.
I liked the premise of the rebels fighting against a superior enemy but always against the odds and with sacrifices, it's more grounded and realistic on how rebels would realistically fight against any oppressor. The Liberator and teleportation gives them a technological advantage, but it isn't enough to make them overpowered. With the current AI development, the series take on AI is refreshing in the sense that AI isn't always subservient to humans like the ships computer, but especially with Orac isn't always aligned. The seventies and early eighties we're also the time of more dystopian SF, Soylent Green, Mad Max, Logan's Run, Silent Running, etc we're a product of the zeitgeist and mood at that time, Blake's 7 fits in.
Actor wise Paul Darrow and Michael Keating steal the show with their performances, but the rest of the crew is hit or miss. It's the same with many other tv series with a larger regular cast, writers tend to gravitate to certain characters, they don't always get the chance to grow. It's a shame that TV at the time wasn't highly regarded, stage plays and movies we're better career wise, nowadays they could have made a better career with it.
I really didn't mind the ending as it fits the premise of the show, but like other tv shows I have a personal distaste for open endings or unsolved mysteries, when there is a story I always want to know what happens next. TV has always had this problem because each season is almost always separately renewed and writers mostly don't start writing until it is.
I heard about rumors of a remake/reboot, but I really dislike them in general. Like all cultural things, things are best borrowed and improved upon, not simply copied. I would like to see more SF series which borrows Blake's 7 thematic setting. The SF show I regard as my personal all-time favorite so far, Farscape, borrows a lot of themes from Blake's 7 and it really improves upon it, I highly recommend it if anyone hasn't watched it yet. Battlestar galactica is one of the few exemptions of a (soft) reboot which largely succeeded imho, but they deviated also on many things, so it can be done but I would be difficult. Especially because many tv writers don't like working with existing material, they want to inject their own stories and creativity often changing things for the worse or even having nothing to do with the original material.