Previously my favorite scifi show was Babylon 5 but in the middle of the last season something happened to the writers and the show just sort of petered out.
I think the problem there was that for a while there was a real possibility that B5 might not be renewed for a fifth season. JMS pushed to get some of the plot threads completed in the fourth just in case there was no renewal which left the fifth season feeling a bit empty.
Agreed. IIRC, nobody knew whether there was going to be a 5th season, so they had to have season 4 potentially end the series. Then when it did get renewed, they had to scramble for plot lines, not entirely successfully.
But Severed Dreams is still one of the finest SF episodes ever.