Breja: Honestly, I think Expanse is more uneven than B5. First season is good, seasons 2&3 truly great, then after it moved to Amazon the quality starts to dip, with season 5 being by far the worst afflicted. There's a very noticeable demarcation line between the SyFy and Amazon seasons. Still a great show by any measure, but I feel like B5 was far more consistant in quality (and overall better, though there's obviously a lot of subjective stuff in such comparison).
For me, the first season started a bit slow, then it found its rhythm and it was a good ride all the way through, pre-Amazon and post-Amazon.
I find the show manages to transition through a changing set of surrounding characters extremely well (and the circumstances of the surrounding characters that stay evolve interestingly) in a way that might actually happen in real life (where the cast of meaningful characters changes quite a bit).
In a way, it feels a bit like Game of Throne in space, which was a winning formula for me.
Breja: Firefly neatly sidesteps the issue of consistency by only having 14 episodes :D
Be that as it may, the whole 14 episodes were really strong. Babylon 5 had some filler episodes quite early I recall.
It felt like Firefly was sticking to a tight plan. It felt like Babylon 5 had a plan for a show maybe half its length and needed filler to fill all the space it had.
Breja: I rather liked Crusade. Yeah, it's nowhere near as good as B5, but I still found it an enjoyable show, and if it lasted longer it might have been something more too.
I recall reading about a show called Crusade after the fact. I guess I should watch it at some point to complete my experience.
Atlo: Firefly is pretty much the opposite then. TVTropes even has a trope named after this: ''The Firefly effect''
''People don't watch because they think the show will be canceled, and then the show is cancelled because no one is watching it.'' I don't know if it is better or worse, but I learned about Firefly years after it was all over (I started backwards watching Serenity, maybe in 2010 and then learned it was based on a show called Firefly).
The actors are kind of old now, but I'm still hopeful that they'll do an animated series with their likeness at some point.