b5 starts a bit slow but season 3-4 are, i think, some of the greatest sci fi television or just television period.
What I've said to people who I've talked to is similar, but a bit different: I think that Babylon 5 is probably the best SciFi that's been filmed (whether on TV or in movies). The depth of the characters, the depth of the story, and the follow through are all exceptional. [That is especially true if one mentally shuffles seasons 4+5 together... since Straczynski was told that the show would be dead after season 4 by the network, he had to cram the conclusion to the Earth war all into that one season, and eliminate the Psy war. He intended them to overlap, just as the Shadow war and Earth wars overlapped. Instead the fifth season has an almost 'tacked-on' feel, though I'm sure it would not have, had he been given the five years initially programmed for the one, massive, highly-interwoven story.]
The only problem I have with re-watching it (the next time will be my fourth I think) is consciously setting aside roughly 90 hours for one story.

It is, actually, the only science fiction that originated in an audio-visual medium where I have cared enough about the story to actually read books derived from it (the excellent - but roughly War and Peace-length - trilogy explaining what happened to Sheridan's son, Londo and G'Kar that was outlined by Straczynski and written by Peter David. [One of the few writers to be allowed to script an episode of the TV series (the one dealing with Londo's wives), and whose run on the comic
The Hulk was often extraordinary. But I digress...

[And, yes, for those in the know, that last line was deliberate.]])
I liked Christopher Franke's music for the series, some of it independent of the series (i.e. some works out of context). And for me, the fact that they were the first to try to go with all-computer effects, and pulled it off as well as they did, was remarkable in those days, when everyone else was still 'playing with toys'.

Oh, and this from Wikipedia, for those comparing B5 to DS9 (keep in mind: DS9 was still my favorite Star Trek series... possibly for this reason):
Star Trek: Deep Space Nine controversy
The pilot episode of Star Trek: Deep Space Nine (DS9) aired just weeks before the debut of Babylon 5. Babylon 5 creator J. Michael Straczynski indicated that Paramount Television was aware of his concept as early as 1989,[57] when he attempted to sell the show to the studio, and provided them with the series bible, pilot script, artwork, lengthy character background histories, and plot synopses for 22 episodes "or so planned episodes taken from the overall course of the planned series".[58][59] Paramount passed on Babylon 5, but later announced Deep Space Nine was in development after Warner Bros. announced its plans for Babylon 5. Straczynski has stated on numerous occasions that, even though he's confident that Deep Space Nine producer/creators Rick Berman and Michael Piller did not see this material, he thinks Paramount may have used his bible and scripts to steer development of Deep Space Nine.[60][61]
It's funny, my brother and I were discussing TV vs. Film a while back (I came down heavily on the side of TV, as the ability to develop relationships between characters, and between characters and their environments can happen in a more believable fashion, not being crammed into usually a 90-120 minute timespan). But I do acknowledge and appreciate the occasional remarkable film that has a believable progression during its time-frame. [I don't know if anyone saw my photos of my film collection elsewhere in the forum, but they were not all RiffTrax'ed films.]
I agree with Imrahil: most so-called film SciFi tends to be
loud and explosiony and dumb
and - dare I say it - rarely
actually SciFi, usually what
calls itself SciFi in film and on TV tends to be 'Fantasy' or 'Action' in Space... that's not the same thing.
Well, as anyone that knows me knows, the fact that this post is as long as it is (and that some sentences never QUITE seem to end, with multiple detours before their conclusion

), I'm waaaaaaay past my capacity and should've already been in bed trying to sleep. [It's ~6:15am now.] So I'm outta' here.