The first time I read this, back in the 80s, I was around the same age as the characters in the book. Maybe a little younger. (and I really wanted a Lucky Unicorn of my own that I could carry in my pocket). The book popped up in my feed recently. I remember really liking the story back in the day, so I decided to revisit it.
And it was all right.
Before I launch into my personal review, I want to comment on things others have said: Specifically on how mean and bratty and unlikable and, well, straight-up awful the characters are. By today's lofty standards, the way Emily and friends behave toward their peers would be deemed unacceptable. In books published today, characters would never make fun of a classmate for wetting the bed or being a crybaby or being overweight or whatever. And while I totally agree on the meanness factor there (and I in no way condone that behavior), the fact remains that it's real, whether readers like it or not. Because the fact remains that kids can be mean and unfiltered. And they have an uncanny knack for finding one's most sensitive places and poking them with a sharp stick. What's more, they can turn on you out of nowhere. Just because they're your friend today doesn't mean they won't be busting your chops tomorrow. This book and the way it depicts such behavior is actually pretty authentic. Also, the fact remains that it was published in the 80s when things weren't so...I was going to say "polite," but I suppose "censored" is a more fitting word.
Anyway...
This book focuses on Emily. She's not the smartest or prettiest girl in her class, but she IS the fastest runner. She prides herself in that. It's the one thing she feels she has going for her. All this changes when new girl Dawn arrives. Dawn is pretty, smart, and she becomes instantly popular (also, she's a bit of a snob, if you want my opinion). Worst of all, she's a faster runner. Emily is both fascinated by and jealous of Dawn. And Emily wants very badly to be Dawn's BFF in the worst way...but she also kind of hates her. This Frenemyship (is that even a word?) is pretty much the basis for this entire book. And things only get worse when Emily's Lucky Unicorn disappears. The prime suspect? Dawn, of course. But can Emily prove it? Much pettiness and nastiness ensues, because, like I said, kids can be mean. But the girls (tentatively) patch things up (sort of). That doesn't mean everything between them is all rainbows and sunshine from now on, though. But Emily does eventually get her Unicorn back.
Overall, not a bad read. It had its moments. Did I love it as much as I did when I first read it? Of course not! I was probably all of 7-8 years old on the first go-round and just starting to have the skill (and attention span) to read chapter books. So, at the time, I really had nothing to compare it to. I'm not even sure I'd been fully introduced to the Ramona books at that point. Honestly, I think I just liked that a character had a Lucky Unicorn...which I still think is pretty cool. But like I said, not bad. Not bad at all.