Online critics are motivated by a need for attention. They want you to notice them and to censor them and to fight back. That's the goal. So ignore the harshest ones.
But don't ignore what they say. This is valuable feedback. It's free and it's quick and it's useful. It points to a thousand ways you can dramatically improve your product -- before it's too late. If you quickly embrace the essence of the feedback (without defensiveness) then you win.