People have criticized that the first two books in the Harry Potter series don't showcase her best work. In a way I have to agree with them. They are quick and enjoyable reads, but Philosopher's Stone has some inconsistencies and Chamber of Secrets can kind of drag in some parts. However, in my opinion, by the time you get to Book 3 (Prisoner of Azkaban), you can clearly see the richness of her writing from the characters and their back stories to this overall sub society (Wizarding World) that she has created.
I think what I love best about Rowling is that she created this whole other world down to the littlest details much like in the fashion of C.S Lewis with Narnia and JRR Tolkin with Lord of the Rings.
The great thing about her 'world' is that you can get lost in it and totally get immersed into that world, so much so that words like 'Muggle' and 'Patronus' become part of your everyday language (or maybe that is just me.)
Rowling has such a vivid imagination I can't help but be jealous of how detailed it is and how well she transferred what she saw onto the page for others to see and enjoy.
Aside from this fantasitcal world she has created, the characters in her series, regardless if they are good or evil, are flawed. Even our hero, Harry Potter, who can be arrogant and a bit of a martyr sometimes, is wonderfully flawed. But he eventually learns from his mistakes, sometimes the hard way and at the expense of others.
I also love that the overall importance of love and friendship is the message throughout the books. What separates Harry from Lord Voldemort are his [Harry's] choices and his capacity to love, and understand its importance in his life. I like what Stephen King says about Harry Potter:
"Harry Potter is about confronting fears, finding inner strength and doing what is right in the face of adversity. Twilight is about how important it is to have a boyfriend."Edit to add: I started reading the Harry Potter series when I was a year into TTC. When everything with trying to have a baby became too much; I could escape the ickyness of my reality and lose myself in Harry Potter's world. It was by far the best written distraction I had until the series was complete in 2007. I mourned the end of my distraction, but you know, the great thing about a completed series of books is that they are still there to read from the beginning again. In my opinion, the series never gets old.
— Stephen King