The problem with series five wasn't the lack of good storytelling or characterisation, but image. Having most of the arc threads tied up by the end of series four left the action a little flat. Pretty much from the middle of the third season up until the end of the Earth civil war, there wasn't a break in the action at all - no stand alone episodes that had nothing to do with the arc. Once the Earth and Minbari internal conflicts were resolved, the events that took place afterward seemed to be an epilogue of sorts. And with the cast changes, it gave the fifth year a sort of arc of its own (i.e. Byron's teeps, Garibaldi's relapse and Londo's descent). We the viewers were spoiled by the overstuffed episodes that we became restless in the face of deep exposition.
Personally I think, if anything, there were too many different plot threads in the fifth season. Having the benefit of retrospect after reading the Centauri and Psi Corps trilogies, each of those topics could have gotten a full year's treatment. Simply stated because a good deal of the plot threads in both cases were left dangling at the end of series five, especially the Telepath War that always looms but of which details are NEVER revealed.
To a degree, I agree with Mr Doyle that the plug was pulled too soon on B5. If JMS only wanted to do five years, I can't slight him for that, but there was an awful lot left of interest when the series ended. So if anything, the fifth season suffers for it - unanswered questions and the aforementioned lack of nonstop action.
