Will they sell you just four and a half?
I haven't seen B5 since its original run but I loved it. The first season was cheap, badly acted and I almost gave up on it very early on if I remember correctly. With almost no warning, it became clear that there was much more to the show than was initially apparent. This was a show with a plan. A real plan (not a crappy fake plan like poxy Lost or whatever). Little things that had been dropped in all over the first season started to become big things and it grew and grew getting better and better. Season three was just about my favourite television ever made. I was in Norway at the time, where it wasn't been shown so a friend wold videotape the episodes and send them to me. A stunning show.
Until halfway through the fourth season.
If you like sci-fi, I'd say go for it. If you don't, well, you probably wouldn't be looking to buy it in the first place.