Always a sci-fi fan so I hooked into Babylon 5 as soon as it began in the early 90s. Immediately I was interested in how it was both darker and DEEPER than Star Trek TNG. And I was intrigued how many of Season 1's episodes were planting the "seeds" of a huge mystery that I sensed was not going to be resolved soon or easily.
Then in Season 2, the seeds started to blossom. Wow, was I hooked! Every week I wanted to see what more the main characters discovered and how each of them were changing as people from what they were learning. Yes -- true character evolution! (The character Londo's evolution, by Season 5, is almost Shakespearean in scope and depth).
For new viewers, I have the following advice: (1) this was the 1st TV show to use CGI for all of its space effects -- no models -- so cut it some slack 'cause the software was nascent back then; (2) Season 1 is rocky with both wooden acting and over-the-top acting I found distracting, and uneven story-telling but LOTS of info you need to appreciate the following seasons. Hang in there because things go into high gear in Season 2 and then Season 3 blows the roof off. It is no wonder how most sci-fi TV today utilizes the serialized story-telling Babylon 5 pioneered. It is effective!
One last piece of advice: I've seen suggestions to watch the pilot movie "The Gathering" and the prequel movie "In the Beginning" before starting Season 1. My recommendation is (1) don't bother with The Gathering (it only offers a little toward the main story while lacking character continuity with the series) and (2) DO NOT watch In the Beginning until the end of Season 4 -- it is a huge spoiler for several Season 1 through 3 story lines.