Babylon 5 redefined TV science fiction, so why isn’t it better known?

I have to admit, watching it again after the revelation that Michael O'Hare was written out of the show due to mental illness puts the whole thing in a very different light. The introduction of Bruce Boxleitner in the first episode of the second season always felt a bit weird, and now the reason is clear. It's hard not to imagine how it could have been, as a lot of things in the story would have been much stronger if Sinclair had remained the commander of B5 until he went back in time (which I imagine would have happened later in the series). A whole bunch of major plot events in the later seasons would have made more sense with Sinclair, foreshadowing in the first season had to be re-done in the second season in order to fit Sheridan into the story. It's especially apparent since Sheridan is IMHO one of the weaker characters in the series. Most of the actors grow into their roles, but Boxleitner's Sheridan never seems to get comfortable.

And of course, the pacing gets really weird at the start of the fourth season. They race to finish the shadow war plotline in the first few episodes, but I suspect that was supposed to last the whole season. Then they have to power through the earth civil war which really was supposed to be fleshed out better before kicking into high gear.

B5 is a great show. If you haven't seen it, you should. But man, I'd like to see the B5 that could have been, where Sinclair was the commander and the writers had time to flesh out the end of the shadow war and earth civil war storylines properly.

Extensive use of CGI to drastically reduce set costs. The core of the B5 show takes place on relatively extensive sets that are reused throughout the series, with one-off locations presented with large amounts of composited CG backgrounds. All of the space and planetary footage is rendered, and this choice of setting (simplified lighting and shot composition) played heavily to the favor of the tech at the time--I think most if not all of the work was done on Amigas and Video Toaster.

Heavy interaction with the fanbase using Usenet. I think that B5 was probably one of the first times, if not the first time, that fans got to significantly interact with the folks who were creating a show in a meaningful way. These days, it's pretty obvious and common to have shows use their online presence and discussion panels and whatnot to create organic advertising, but back in the day having JMS show up and answer questions and explain why things happened the way they did was pretty amazing.

Tightly and long-plotted series storyline. Compared with basically any of the Star Treks (and DS9 is quite arguable because reasons), Doctor Who, Buffy, X-Files, or other contemporary shows, B5 Had 5 years of plot to get through and managed to do so. Every episode (barring some crap chunks of season 1) brings in a new plot line, advances an existing plot line, or closes up a plot line. This is a series that really bears watching twice specifically so that you can see how seemingly little things telegraph well in advance important later points. At least through season 4 I never felt that there was an ass-pull or a moment where the narrative didn't know where the hell it was going. I felt like the writer(s) respected me and were going to take their time to weave a good narrative, however long that took.

Genuinely terrible characters and no-win situations. Nowadays it's become somewhat in-vogue to have darker and edgier storylines, but at the time seeing a show willing to do just really evil things (killing children) and having horrible tragedies occur (depicting the permanent loss of at least one alien race that we'd gotten used to seeing around) was rare. Not only was it rare, but it did so in conjunction with a fundamentally optimistic view about people and the future--which is exceptionally rare these days.

Displaying competent and important women and LGBT characters. Delenn is an obvious example for her work with the Minbari and later actions, but Susan Ivanova is probably one of the most capable yet human characters I've seen in television science-fiction. Additionally, the way the show explored her interactions with Talia Winters was basically pushing those themes about as far as you could in television at the time it came out.

Honestly, the only show I'd put in the same ballpark would be the anime epic Legend of Galactic Heroes. I'd strongly suggest, if you enjoy these things, treating yourself to B5 seasons 1-4 and seeing just how well done this material can be even in the absence of large budgets or well-known actors.