Sometimes I come across reviewers who claim to be "objective". They claim they review things without bias. I cringe every time I see this.
Why? Because to be a truly objective book reviewer, you'd have to be a robot. For the rest of us human beings, there is no such thing as an objective review. There is no way to be unbiased when reading.
Think about it. Whenever you read a book, you bring your entire collection of experiences along for the ride. You bring your hopes, dreams, fears, feelings. Everything that you've ever done, seen, known, or felt contributes your enjoyment (or lack thereof) of a book.
Say someone struggles with self-image issues. Whenever this person reads about a character with the same problems, they have a way to connect to the character. This might be the deciding factor in whether or not this reader enjoys the book. A different reader might read about this character, but since they've never struggled with self-image, don't have that same connection with the main character. They end up disliking the book.
These two readers had different opinions of the book. The difference lied simply in the experiences one reader brought to the reading.
Whether you know it or not, when you read a good book, things speak to you. Characters address fears that you might not be aware you have, but they're definitely there and because of this, the book has more meaning for you. Maybe you desperately needed a book with a happy ending, and one certain book came along and delivered it for you.
This is why it isn't possible to be an objective reviewer of fiction. No one can judge completely on writing, plot, or characters, because there are so many other things at play in a novel without us even realizing. Again, you'd have to be a robot. But robots couldn't possibly enjoy fiction (if they could enjoy), for these same reasons. They have no feelings, no experiences with which to connect with the book. There'd be no connection, there'd be no spark. For a robot, a novel would be flat and meaningless.
Just because you're a subjective reviewer of fiction doesn't mean you're any less credible as a reviewer. In fact, it makes you more credible to be aware of this fact. Don't shy away from letting your feelings and experiences contribute to your enjoyment of a book.