I really enjoyed this story and was totally taken into it, but with some caveats.
I guess, not being an expert in any sense of the word, that it must be difficult to write a series novel. The pull must always be to revisit a character's backstory, to remind us what that character has done, or had done to them. So I was a little forgiving at the beginning, especially as I hadn't read any of Brenda Novak's previous novels. I shall say that Evelyn's past sounds terrifically awesome in its gruesomeness, but being reminded of it constantly grew a bit tiresome about halfway through. As did the I can/I can't enter a relationship; I get that Evelyn has issues, I understand why and I understand the dichotomy in her mind, I don't need it to be related back to her encounter with Jasper all the time. Maybe give the reader a little credit that they could decipher it, especially if it's already been explained previously in the book. It might just be me that finds this irritating though.
Also, and this is my last negative honestly, I personally found it a little choppy towards the last few chapters. The 'not described' sex scene seemed a little extraneous, and the oh-my-goodness meeting of good vs. bad was a little bit disappointing, just because it was a bit...(I'm struggling to find the right word here)...a bit over-too-quickly I guess. "I did this because of this, so blah blah, fight, fight, blah, blah", that sounds really bad, it isn't, I think that it just could have been better, more suspenseful, built up a little bit more - it was just too good a scene and it was felt a little thrown-away, which was a shame.
Gosh, sorry, that was a bit long; perhaps unnecessarily so!
I did think that Her Darkest Nightmare was a good, no a very good, story at its heart. Like I've said, the Evelyn vs. Jasper backstory is a great one, very compulsive and a terrific basis for this one. It made for some truly great suspense. And, apart from the final showdown, it was packed with tension, helped no end by the remote setting of the prison/experiment centre of Hanover House.
The patients/prisoners were interesting in a psychopathic serial murderer kind of way, and I wasn't ever sure whether Evelyn was being prepped as the next victim, or helped, albeit in a perverse way. The relationships between the main characters were believable and natural, though more could have been made of some of the characters. Though, of course, this is a series so I acknowledge some of that may have been done in a previous book.
It has enough twists and turns to keep you guessing who is behind events at Hanover House, and I cared enough about the characters to be invested in who was playing for the wrong side. The actual, true ending to the book was great, and I thought an excellent way to finish off, leaving me definitely wanting to read the next book. Her Darkest Nightmare is absolutely well worth a read.
