A lot of the more generous reviews are suggesting that doing justice to five Doctors and five companions is some Herculean task that no one could manage, which I think is a bit much. Nick Briggs evidently couldn't manage it, even with the get-out-of-jail-free card of time folding in on itself, but it's not like no writer in history has handled a ten-character ensemble in a two-hour story. There are almost as many in "The Five Doctors," which is only 75% the length of The Light at the End
, and I don't think anyone would argue that script shows Terrance Dicks to be the world's greatest master of narrative structure. He was simply up to the task before him, and Briggs wasn't.