This review will contain spoilers!
In many sentences:
The Borrowers was a fun, cute little story that I enjoyed reading. I didn't feel like there was a lot of depth to it, but the setting was well-realized and imaginative. I think it would be a great book to read with young readers, as the adult would enjoy it, and using the excuse of Borrowers around the house afterwards would be a lot of fun.
I will say that the end, in which Aunt May implies that her brother may have made up the story about the Borrowers to be great. It put a huge smile on my face to think that Aunt May would have been tricking her niece in that way.
As I said above, there's not much to The Borrowers, but I look forward to reading it with my children when they are older, and the subsequent "imagining things around the house are disappearing because of Borrowers" play that will ensue.
Mary Norton the First Line of The Borrowers
Mary Norton the Last Line of in The Borrowers