The cast changes were basically all forced on JMS by outside factors. He's actually quite well known for his good working relationships with actors, making accommodations for schedules, asking their advice on dialogue choices, etc.

O'Hare's worsening mental health issues are the most well known but there were many others, like Furst's short-lived TV sitcom attempt which meant he was basically just doing cameos on B5 for awhile before coming back full-time.

Na'toth's first actor had to stop playing the part because of health issues with the Narn makeup. She came back for a significant guest role as a human in a later episode.

Thompson left largely because she wanted to try a journalism career, which she turned out not to be very good at. There's clips floating around on youtube of her work. Her divorce of Doyle was the big factor in why she didn't return.

I think Boxleitner's slightly hammy style is perfect for the type of character Sheridan becomes. He's a good fit for the long arc even if it seems like a jarring change at the moment.

Sheridan's arc and development ends up being pretty great overall, and what they do with Sinclaire later ends up being such a great payoff to losing him, in my opinion. The show is just a masterpiece in so many ways.

The 100 also suffered from losing too many original cast members. I get it’s a survival show at its core but like you still need interesting characters lol

Boy oh boy! You are gonna LOVE Season 3!

Also, "fucked by cast changes" is the tip of the iceberg. Some people think the show was cursed. When you're done with the series, look up the status of the main cast as of today.

Also again, check out this archive: http://www.jmsnews.com/ It has JMS' thoughts on the show, posted back when internet newsgroups were popular.

Uh-oh, I'm apparently only 4 episodes away from this one...

I'm committed at this point, but main oh man do I hope it gets better. I feel pretty tolerant of the tropes of 90s television, but you get jerked around a lot in early Babylon 5. And I get that they don't have the budget to be doing episodes with their alien cast every week, but it kind of stands out how they will just be gone for several episodes.

I do appreciate the ambition, it's pretty impressive that they managed to make this show. But it makes the flaws that much more obvious.

Michael O Hare was just a straight up better lead actor than Bruce Boxleitner.

Definitely. I'm glad we got the one season of Michael O Hare, and I kinda thought they didn't take advantage of the transition for more storylines where the new crew had to warm up to Sheridan. It feels like I'm taking longer to warm up to him than the other characters (Delenn, especially)