I voted I don't care first, but then, reading your post, I understood that you meant "criticism", and I changed my voting accordingly.
There are, IMHO, 2 types of criticism:
Constructive; "I like your app, but I would implement this feature in a different way, and add that other feature to it."
Destructive; "Your app is worthless, it does nothing it claims to!"
Then, there's the semi-constructive or neutral criticism; "I like your app."
I welcome every constructive Critic, because it's meant as a way to improve the product, and points are made that can lead to a really great product.
I usually don't give much attention to destructive critics, since normally they have no valid arguments and only want to "say something".
The neutral ones are just that, and receive absolutely no attention.