There's absolutely nothing wrong with writing all reviews with a positive slant. If there's anything wrong with a device/product that ends up hampering the enjoyment of it... fine - discuss it. Otherwise, why is being overly critical a good thing? People use products to have a good time, so shouldn't the review be coming from that angle as well...? That makes much more sense to me.
I don't buy a phone because of things it doesn't do. I buy a phone because of things it DOES do.
I don't buy a phone because of things it doesn't do. I buy a phone because of things it DOES do.