Advice
Don't be discouraged by poor scripts, as they are an opportunity to understand and express what makes something boring, unsatisfying, or trite in a way that goes beyond blurting "it's just bad." Being able to defend your notes with direct references to dialogue or scenes (and citing their page numbers) is a good habit to form.
Ultimately there is a lot of subjectivity involved with assessing the quality of a script, so try to check your biases against certain genres and approach your coverage like it should be received with a grain of salt, not as gospel truth. That being said, still use strong and concise language in your coverage; don't invalidate or downplay your opinions as you express them, just express them knowing that others may disagree, and that is okay.