I have only come across one series by an Indie author that is either free or DRM-free that I have rated 5 stars: Shayne Parkinson's
Promises to Keep quartet, which begins with the free
Sentence of Marriage. I reviewed the books
here and
here.
For fiction to rate a 5-star review from me, it must be so compelling that I can't put it down, causing me to continue reading long into the nigt (early morning hours), plus it must compel me to write a review recommending it (something I do not do often), plus it must still make me think about it months after having read it. I think 5-star books are few and far between. There are a lot of 4.5- to 4.9-star books, but a book needs that something extra special to warrant the label of perfection.
On the commercial side of the equation, the closest to 5 stars but not quite there have been recent David Weber books and the
Imager Portfolio series by LE Modesitt, Jr. I'd give Weber's recent books a 4.5 rating and the Modesitt series a 4.7 rating. They were good reads that kept me burning the midnight oil and are worthy of recommendation (but not the time to do a full-blown review), but they are now forgotten in the sense that I no longer think about them or their stories.