I didn't even know he was raised by humans. That's just weird. I thought people liked him cuz he was fiercely Klingon or whatever.
He is though. He was raised by his human adoptive parents since he was five or six, but chose to fully embrace his Klingon background since, in spite of the friction that sometimes results from that in a Federation environment. He's patterned himself after the ideals that represents to him, which is why he's so different from the average Klingon - more idealistic, less fun, and very dedicated to his ideal of what it means to be a Klingon warrior, because it's something he's always had to prove, both to humans and other Federation types as well as to his fellow Klingons.
It's a real phenomenon that in some circumstances, people who move from one cultural context into another will double down on things that they feel define them as different from their new social context, because it becomes more important and also more vulnerable to them as a part of their identity. Klingons are also still discriminated against in the Federation, which probably means he has to struggle to maintain the validity of his identity above and beyond just boundary maintenance.
So that's the two-by-four up his ass. I honestly have no idea why people
like him, but I recognize that people have different experiences and respond differently to particular characters.
