I really enjoyed the Harry Potter books... I thought it was a great story... and epic of good vs evil told in a manner that was entertaining and could capture the imagination of child and adult alike.
However, I how no idea all of the symbolism and mythology and such that she put into this series until I started listening to the SQPN: Secrets of Harry Potter podcast. It goes into some of this stuff.. for example many of the characters names have a deeper meaning or tie to some greek myth or religious icon...etc...
I am sure a lot of what they say in the podcast is speculation... but much of it makes a lot of sense... so, it impressed me even more the thought and planning that she put into this series.
I have no idea if JK has more on the horizon.... but I look forward to her next efforts. I have no idea if she can top Harry... but I for one will be reading her next book (if there ever is one) even if I have to buy it in paper. (We bought 5 paper copies of The Deathly Hallows and the audio book version on CD on the release date.)