Quentin, or Q, is very intelligent just like his two older half-brothers, as all Holmes boys are.
He is able to make well off deductions but not as well as Mycroft or Sherlock.
Quentin does, however, have more heart than Sherlock or Mycroft. He’s willing to show genuine sympathy and compassion for those who deserve it.
Despite all of his mild passive-aggression and sardonic remarks toward his brothers, he becomes very over protective of them when something becomes a potential threat. But he wouldn’t dare tell you that, if you asked him.