It's hardly fair to judge a show when its first season has barely started, so consider this more of a "first impression".
The basic concept of a normal family trying to adapt to having superpowers is intriguing on its own; and the characters so far have been likable and well-acted.
The problem I have is that the things they have done do not always make sense. Jim has become a vigilante despite the worries of his family, not to mention the fact that what he's doing is illegal and he (and his lawyer friend) know it; even worse he hasn't really been making much of a difference- just catching a few crooks. With the exception of the superpowered ones, the police doesn't really need his help.
Why is JJ keeping his powers a secret from his parents? I know he's trying to impress people and doesn't want his parents to stop him, but he keeps getting in one mess after another, you'd think he would have caught on that by now. And how big a hypocrite is his sister Daphne about warning him against abusing his powers then abusing hers? (Not to mention her "plan" to blackmail the liquor store owner was VERY dumb.) So far the only one who hasn't done anything too stupid is the mother, Stephanie, and that's mostly because she's been given the scientist angle, investigating the origin of their powers.
Even the supporting characters act dumb, like JJ's teacher, who is starting to fall into the "resenting teacher" role. (Stephanie's male scientist partner is also like this, openly showing hostility without thinking it might make HIM look bad.)
And we also have the super villainous conspiracy going on in the background. Are the producers afraid the show wouldn't sell without it?
In general, the show seems to be suffering from the same problem that Heroes
had in its later seasons: the plots are too comic-book like for a show that's supposed to be more real than that. The ideas are good but they're not being handled well. Doesn't mean the show cannot improve, but right now I'm not impressed.