They should have made the attempt of creating a feel for those 100+ people family developing aboard. All we get is a couple of episodes with random low level crew members who are never heard of or seen again. And probably, if you watched every episode and counted the crew members, you probably get a thousand different people. It would have been quite a task to keep 100 extras over the course of 7 years, but they should have tried it. And instead of doing a "random crew member who has never been seen before returns from the dead" episode, they should have created a short arc about it, with one episode introducing the character, another episode killing him off, and another episode dealing with the return. There also was an episode where the Doctor gets mad because he didn't save the life of a random crew member who, in that episode, EVERYONE seemed to know very well. And that is just silly because WE, as the audience, never knew her.