The whole point is that of a subjective analysis, with infinite interpretations which aren't objective views of the text, but a product of the interrelationship between: the text, the context of the text's writing (inc authorial intent), the analyser, their context, and the context of the academia around the text pre existing. These aren't objective measures, but the aim is to have something to say, to have enough insight into the world to link ideas up and make something up that sounds convincing.

Saying the book isn't as good as other people said it was isn't that, and it isn't really very useful, even as a personal opinion, and is completely missing the point of the exercise.

That is because that statement is both not useful in the context (you're there to pick it apart) and reflects pretty badly on your understanding, clearly the text has some depth, even if not consciously included, to be analysed. If your conclusion was "rubbish" when you're meant to be making a point about subtext, you're failing, its pretty simple.

People include subtlety in their art even if they don't intend it. Things can not be fantastic but still reflect society, the author, your own experience, which is the point of literature analysis.