I'm not much of a deep thinker when watching a half-hour comedy show, but since you asked, I'll try to answer.
Obviously I find the mom to be completely awesome, but everyone seems to agree on that.
The dad is pretty solid in my mind too, although not to her level. I find him humorous and fun to watch, and perhaps it is The Interview that makes me like him more than I should, I can't say. I like him though. This last episode, for example, where he kept telling the exaggerated accounts of his father, was pretty decent for me.
I don't mind the main child actor, and my capacity (not to mention desire) to determine acting ability is obviously far below most other people's. It takes an exceptionally bad performance (Kristen Stewart in Twilight, for example) to make me even think about someone being a terrible actor. Otherwise I might just dislike the character more than anything. And I don't have a problem with the kid. He's a chubby little asian kid trying his hardest to be a stone-cold pimp in junior high (or whatever). And failing miserably. Like pretty much every kid that ever existed. Granted, I think the majority of the other school stuff is stupid as fuck, particularly this last episode. However, if it provides the impetus for the rest of the episode (getting money for Shaq-Fu, finding a porno tape), I can put up with a minute or two of it.
The two younger brothers don't bother me either, actually. Every once in awhile one of them makes me laugh. And the one with the constant girlfriends actually is a decent running joke for me at least.
Grandma is lame, but I get her purpose. Neighbors and restaurant employees and fellow students are all similar, where they need to be there so you aren't just seeing the family in a bubble. And sometimes they provide a good laugh, or a good place to bounce a joke off of. Most of the time they kind of suck, but like I said, you have to have them. If they were better it would be great, but they aren't ruining the show for me either.
Often I guess I would have to say that it is the mom, the dad, and the situations/stories that they sometimes find themselves in. Hell, the part where he was trying to get a hug from the hot neighbor was funny enough for me, even though that's nothing special.
Is it high quality entertainment? No. I'd rather watch Brooklyn 99, Archer, Broad City, Silicon Valley, Workaholics, You're the Worst, and probably a few others I'm forgetting. I wouldn't give it an 8.3 if that's what you are saying it has. But I don't feel like I wasted my time after watching it either. I'm easily amused though, so perhaps I'm just not discerning enough compared to everyone else.