I hadn't heard of this series before stumbling upon some paperbacks at a library sale, which I snagged for my LittleFreeLibrary. I figured I'd read one or two first, and I did (#5 and #7). Checking out the series. I saw that audio was available for the first few books. I borrowed this (Hoopla) and experienced it in audio (although I also grabbed the Kindle copy, I didn't have this one in physical format). 

While these don't need to be read in any order, they feature all different breeds of horses, set in several locations and time periods ... I was glad to read the "first" book in the series (even if I didn't read it first). 

This one starts right at birth. Female horse (the other two I read featured boy horses).  Each story I've read (so far) has human interaction, and a connection with a special human. 

From an adult perspective, I think I like the appendix at the end the most. After we/the reader gets the fictional story/setting, the appendix outlines facts and additional information. This one especially, I learned some new things ... the tölt gait and that Iceland doesn't allow ANY horses coming in (keeping the breed pure). 

Hard to rate, as an adult reading a book for older elementary - good, interesting, easy/conversational, just enough action. 3.5 for me, maybe my 10 year old self would have rated it higher?