Babylon 5 was originally conceived as a novel for TV, with each season akin to a book and each episode a chapter. However, the show was nearly cancelled towards the end of its 4th season, which is why the season ends with the formation of a suspiciously federation-like Galactic Alliance. This was originally intended to be the end of the last season, but with the show's future in doubt the plot was condensed and the ending moved forward. Elements such as the telepath crisis were left out, which is why the 5th season is so concerned with these events, and at times seems not to fit quite as neatly into the story arc.
Babylon 5 was not without it's hiccups plot-wise; any show with a 5-year run is bound to lose actors, and indeed it did. Originally, the captain of the station was Jeffrey Sinclair, played by Michael O'Hare. At the end of season 4, Claudia Christian left, and her character, Ivanova, was replaced with an initially very similar character, whose name escapes me. Also, the reason that Delenn grows hair between seasons 1 and 2 is not because the plot demanded it, its simply that Mira Furlan was sick of going through excessive makeup for the show.
One of Babylon 5's main problems is that after the 2nd season J. Michael Straczynski started to write all the episodes himself, and while this made for a more coherent story arc, he is terrible at writing dialogue. For example, "That's a bloody awful lot of ships" is an utterly cringe-worthy quote that no genuine Englishman would ever utter. Trust me. Despite this, the show is consistently excellent, with an engaging and complex story, and a rarely-seen level of characterisation. The special effects, although technically not as good as Star Trek's at the time, were far more daring, showing impressive and often huge battle sequences with far more regularity and in greater detail than Trek ever did. The low cost of these scenes meant that they looked a little rough, but they didn't have to resort to stock footage as Deep Space 9 did so often for its Dominion war. And remember, by the end of the run they were working with 5 year old computer technology.
Overall, Babylon 5 was an excellent but flawed show, with a grand vision that had to be compromised to some extent, but that was good enough to carry it through its rough patches.