What I really liked about him was that he represented what is, for me, the essence of Doctor Who. The race of cloned warriors, bred to kill and die...but the Doctor somehow had owing him a penance. What penance do you exact on a creature like a Sontaran? Why, make him a nurse so that now he must heal the weak and sick. Best of all, he ended up liking it, despite his incredibly funny taunting of his patients that he hoped to one day butcher them on the battlefield.
That's what Doctor Who is all about to me: turning the soulless killer into a healer.
And yeah, the idea of him insisting that he breast feed the child was hysterical. I liked the connection to Rory as well. Rory is a nurse, not a warrior.