When I first heard Kindle was adding a lending library, I was thrilled!! After using the library, I'm still happy...but a long way from thrilled.
First, you must be a member of Amazon Prime to access the library. Personally, not an issue as I've been a member of Prime for a long time. Other Kindle users, however, may not be willing to pay the yearly fee of $79. For me, a huge portion of my online shopping is through Amazon so I recoup the fee in free shipping. If the only reason you use Amazon is for your Kindle, it may not be worth the cost.
Second, you are only allowed to borrow one book from the library per month. One book!!! I am an avaricious reader and can finish a best seller in 24 hours. So I have to wait another 29 days before I can borrow another book. On this point, I would have to call this a major fail.
A suggestion from this humble Kindle addict? Instead of the standard "remove from device" option which sends books to your archive, replace it with a "Return Borrowed Book". Once the book has been returned, your access to it would be removed and you would be free to borrow another book.
But the bottom line? Free is free. And you won't get too many complaints from me when it comes to free! I'll continue to borrow my one book a month until I make my way through the entire library.
Have you borrowed from the Kindle library yet?