I think the complaint is he does no rescues or those kinds of heroics in costume, as Superman. I think there's one soldier he whooshes out of the way of gunfire in Smallville.
Eh, I feel like that's way more specific than the complaint is usually made.
At a certain level I think people react viscerally to the ending and end up painting with a broad brush. I mean, there are few movies I've seen the internet have such a knee-jerk reaction to as Man of Steel. It's a flawed movie, but I find most of the time people really go beyond what they need to trying to make a point.