Why it failed
I recently watched all 3 seasons after watching it 20 years ago (still trying to figure out where all the time went), I liked season 1 the most. Hated that Stacy Haiduk didn't return after season 1. Season 2 got too weird, just too far fetched, is it me or Darwin's voice got weird also. Season 3 lost it with the replaced of Captain bridger and the show lost the sense of adventure and exploration and Darwin's voice got even more weird.
I think if they kept Stacy Haiduk, Roy Scheider and still added Kathy Evison later on and stuck to stories of the wonders of the sea instead of talking about aliens and time travel and politics at the time then it would have done just fine.
One things for sure though I hated Commander Jonathan Ford, holy crap what a spineless character, there were so many instances where he just seemed like he couldn't stand up for his crew and had to follow the rules and the secret relationship with Lonnie Henderson because he was scared of what the crew would think just proved that even more. They should have gotten rid of that character completely.