The series is written from the journals of the main characters and, in the beginning of the series, they are young 18 & 19 and the intimate scenes in the beginning of the series reflect that. As they mature and become more comfortable with each other that is reflected in their words and the intimate scenes in the later ones sometimes cross into the realm of erotic.
I have also created a review on each book in the series here on Goodreads but other than the rating they are not a true review. Each one deals with a different aspect of the series and is there to help answer questions or provide "Bonus Information" about the People of Otland Iis, Kerrisha, and her men. Enjoy.
I have also started a discussion thread on Book One with this same topic if you have any more questions.Tales of the Fifth Guardian; Book One: The Beginning