The ongoing story of Agent Callen's efforts to learn about his past and his family have been intriguing, but if a television show is going to stretch such an arc out for so long, there should be a payoff.
Instead, we learn that Callen's grandfather was a member of the OSS during World War II and worked to bring down Romanian Nazis. He married a Romanian woman and they had a daughter (Callen's mother) who also became a clandestine agent for the U.S. government, going into Romania, and eventually killed (after bearing a son) by the Comescu family for her father's and her work again them.
We also learn that Hatty has known this information for a long time and has been withholding it from Callen. This is where it falls apart for me. What possible reason was there to not tell Callen about his family history? If anything, leaving him in the dark about the fact that there is a criminal family that wants him dead would seem to put him in more danger.
The writers have tried to make Hatty this mysterious, almost all-knowing character, who was involved in many crucial intelligence operations for the United States. The revelation that she withheld this information makes her look like a manipulating schemer, without any regard for a character that she is supposed to care a lot about.