I was obsessed with these books at a young teenager. They were one of the first vampire series I read and were the start of what was, and still is a huge love of mine: vampire fiction.
I recently re-read the first three books and while I enjoyed them for the sake of posterity, I found them to be slightly juvenile, partly in the writing, but mostly in the characterisation.
Don't get me wrong, I loved these books as a teenager along with The Secret Circle series and have recently got them all in the library in the school where I work as an English teacher and am always recommending them to my students, but as an adult they weren't something that gripped me particularly.
That is where this book differed, I was actually really drawn in to the characters this time, especially Damon and Elena.
I also think that the whole feel was much darker and more adult than the rest of the books, for example, the idea of vampires being sexual beings is kind of skirted over in the original books, due to the age range that they were aimed at. But that is a theme which is explored in more detail in these books, both with spirit Elena and Stefan's exchange, as well as Damon's growing desire not just for her blood, but his desire for her as a woman.
This book also had a more grown up and mature version of Elena in many parts, who has begun to embrace her darker side and do what needs to be done, even if it is something that will degrade her or go against her conscience. This was a refreshing change from the puritanical girl we saw before.
I also think the large focus on Damon's character is a huge plus for this book. The whole depressed moody vampire who hates what he is was bored and overdone even before Edward Cullen exploded onto the scene, and Damon's character is a refreshing change. Yes, in places he gets a bit soppy, but the reasons behind it are in character and it is nice to see the depth in his character in this book.
If your idea of an interesting vampire is more Lestat or even Eric from the Sookie Stackhouse novels, then you will love Damon.
Also, I always found Stefan kind of uninteresting, so the book benefits with him being absent for a lot of it.
Matt, Bonnie, Meredith and Caroline's characters are pretty much the same, thought Bonnie and Damon's encounters are amusing.
A lot of reviews have spoken negatively about the plot and the bizarre nature of a lot of what happens in the book, but for me it is this which made the book really engaging and unusual. The vampire genre is so saturated with the same old thing it was actually really gratifying to read something relatively unpredictable and bizarre, as well as within it's own mythology.
The only negative thing I have to say from my own perspective is that there is a point in the book where the secondary characters (Matt, Bonnie, Meredith) are running from one disaster to another in a row with nothing in between, which gets slightly silly, and that this often takes away from the dual narrative of what is happening with Elena and Damon (which in my opinion was more interesting) but that is quite minor and maybe just my preference.
In closing, if you liked or loved the original series as a child or as an adult then I would recommend the newest edition to you, but be prepared for not loads of Stefan if he was your favourite, much darker themes and a lot of random supernatural occurrences.
Personally, as an adult, this book is by far my favourite one.