The title 'elementary go series' always throws me off -- I keep thinking it's for like 20kyu or thereabouts (the first book may be, I'm not sure). It's not. In fact, I'd say you'd just about have to be single digit kyu to really appreciate most of them. The reading on most of the problems taxes me, and I'd say I'm currently running around 8-7kyu.
I was surprised to learn so many new things in this book! I thought it'd be a lot of the same, but it's really not. Tesuji are categorized and named, and I've learned maybe a dozen 'new' moves reading this! Maybe not strictly all new, but newly categorized in my brain with a name, which really helps to recall it when you need it.
Loose ladders, knight's move nets, eye stealing tesuji (which only now do I really understand), tons of good stuff!
Just like the other books in this series I've looked at (Life and Death, 38 Basic Joseki, Attack and Defense (good look finding that last one!)), you really need to give it your full attention to grok the book. It's a small book but thickly laden with information.
I'd recommend doing what I did, which is to skim through all the cool new moves and come back to most of the problems later to 'cement' them into your brain.
Now I just need time to read it... or play... or post :P
If you are 20-15kyu, I'd recommend instead Graded Go Problems for Beginners (if you can find them!) and a good proverbs book or two.