I really enjoyed The Immortal Rules, I think that the world-building was nicely done by Julie Kagawa.
Having read the Iron Fey series (and loving it) I was quite disappointed with the spin off novel, so I was a bit reluctant to read this, but I have to admit that her take on vampires was quite refreshing!
The only reason I have not rated it as 5 stars is due to the length of the book, I think there are parts which could have been cut out/shortened (particularly in the middle) which could have kept it at a nice pace without dragging.
I personally loved Allison as a character, it's nice to see someone who doesn't need to rely on others for help and is able to handle her own.
I have seen that there are great reviews for the sequel (The Eternity Cure) so I am eager to continue on with the series!