I've recently read The Service of the Sword and whilst I did quite enjoy Timothy Zahn's contribution, one thing became very obvious to me when I read Weber's story at the end of the collection and that is that Weber's characters were all fully three dimensional - they had good and bad points and the full spectrum between them - whereas the characters of all the others (Ringo in particular) were very much two dimensional; they were either good or bad and there was very little grey area in any of them.
I will almost certainly read this A Call to Duty when I get around to it but I'm not expecting it to have the same sort of depth as Weber's work.