Removing the XP from leaving a review would eliminate 90% of the spam reviews. There is no reason why a single account would need to leave multiple reviews (rather then updating an existing one) for a book so I suggest limiting reviews to 1 per account per book. Also you should be able to contribute to a novel's score without having to leave a comment. 1 star contributing reviews should not be removed, though removing offensive comments themselves is okay. The only exception would be for obvious boting / multi-account from a single IP which should result in bans, not just review removals. At the time of the ban all reviews should also be automatically removed.
The categories for review stars are also bogus. I would suggest a standard ranking system with the subcategories eliminated entirely as the reader should determine what the weighting is rather then preset categories. If the novel is unreadable then that fact would weigh the highest when determining the score such that the other categories make no contribution. For translated novels the translation score should be entirely independent from the novel score so dissatisfaction can be correctly attributed for an otherwise good novel.
Example rating system:
(1 - Highly Not Recommended, 2 - Not Recommended, 3 - Satisfactory, 4 - Recommended, 5 - Highly Recommended)