One of the major parts of Mass Effect 2 are the quests each member of your crew gives you which will allow you to secure their loyalty. They aren't mandatory, and as near as I can tell have no connection to the main plot but do give you insight into the various NPCs and let you shoot guys in the face. While generally fun, a thematic similarity emerges as you play through these loyalty quests.
Warning: moderate Mass Effect 2 loyalty quest spoilers follow.
Miranda: You help rescue her sister from the designs of their overbearing, obsessive father.
Jacob: You go looking for a distress beacon, only to find out that his father has gone mad with power.
Samara: You help her kill her serial killer daughter.
Thane: You help stop his son from committing murder.
Tali: You help defend her against treason charges, which it turns out were actually the result of actions by her father.
Jack: You help her blow up the facility where she was raised.
Garrus: You help kill a former squad mate who betrayed him.
Zaeed: You help kill a former squad mate who betrayed him.
Mordin: You hunt down a former student who betrayed him.
Grunt: You accompany him on his rite of passage. Also, he hates his 'father', the scientist who created him.
Legion: You retrieve or kill the heretic Geth who were working with the reapers.
Aside from the chance that all the writers on the Mass Effect 2 team have some serious unresolved family issues and a history of poor decision making when it comes to friends, there must be some reason why the loyalty quests draw from such a small pool of ideas.
Family provides a convenient narrative shorthand for strong emotional connections, which saves having to invest resources into establishing more unusual significant NPC attachment to people, places or ideologies. In some ways it is understandable, after all if it took an hour or so of conversation and events to establish a crewmate's motivations, most players would not engage with all the stories.
On the other hand, BioWare did choose a science fiction setting littered with alien species. Having all of the species with whom the player has any serious interaction both physically humanoid but also humanlike in culture, morality and emotions feels lazy. The only one of the quests that explores any situation that might be considered 'alien' is Legion's despite seven of your eleven crewmates being from alien cultures.
I'm really enjoying Mass Effect 2, it's as good a game as I've played in a long time, but I think BioWare might have done better by having half as many crew members and being able to spend more time investing in more diverse characterisations.