I think it's because it's De Niro, and because he's a legend that people are critical if he make less than stella role choices. We all know what he's capable of and I do tend to sigh a little when I read about another role in a non descript comedy. I for one would like to see him in a few more meaty roles before he retires. He's more than capable.
I mean let's face it, if it was Rob Schneider making yet another 'comedy' no-one would blink an eye.