As a critic you’re different things to some people; to readers you’re a canary, seeking out what they’re not sure of. To the text you’re talking about you’re either an asset or a massive problem, depending on how you find it. To people who vehemently disagree with you you’re an opponent.
But most of all you’re an advocate. You speak for a text and if you speak well and honestly you will sell people on it or drive them away. So, you have a responsibility not just to the reader but the text. Speak honestly, speak enthusiastically but do speak. Be honest and enthusiastic and funny if you can be, but regardless, speak up.