There are TONS of excellent book series out there, and the most popular of them don't always deserve their fame. Here is what I would rate some of the most popular series of books:
Harry Potter by J.K. Rowling--5 stars
J.K. Rowling fully deserves the billions of dollars she has made off of these most excellent books. Full of rich emotions and adventure, with plenty of thrills, chills, and giggles along the way,
Harry Potter is lovable for anyone, any age. Personally, I've read each of them at least 10 times each, and they never get old. It's hard to say the same about others.
Twilight by Stephenie Meyer--3 stars
While this book has a great story line, the writing is mediocre. I found this series entertaining myself, but only because I'm a complete romantic. If hardcore love stories is not for you, AVOID THIS SERIES AT ALL COST.
The Lord of the Rings by J.R.R. Tolkein--5 stars
Although I do give this series 5 stars, I have to wonder if the movies have any influence on me. I read the first book before seeing the movie adaptation, and I did enjoy it thoroughly, but the movies moved me so intensely that I was compelled to read the rest. They are fabulous, but I wouldn't recommend them to those who aren't up for long reads.
The Chronicles of Narnia by C.S. Lewis--4 stars
This series is excellent for children and reminiscing adults, but can be a bit annoying in their simpleness at times, although I find it endearing. Read it to all your children, however. Especially inspiring to struggling Christians.
That's all I have time for now, but I'll definitely do more later!