The first season is a lot of world building and one off episode stories. They all move forward character motivation and the world, but it is the most difficult part to get through for most people. Once season 2 gets going, it pretty much doesn't stop til halfway through season 5.

I'd easily say that B5 is as good or better than almost any other sci fi show ever made. It's absolutely a product of it's time, but at the same time it is so forward thinking in terms of an ongoing multi season story arc that survives multiple major characters leaving the production with few hiccups. It is almost prescient in some of the scenarios that are explored, particularly in the back half of season 4.

I don't know if another show has done a better pairing than Londo and G'Kar. By all measures, I probably watched B5 way too young, but I adored it at the time and found it amazing on a rewatch a handful of years ago. Typing this makes me want to watch it again