I've been reading and re-reading this series since Slave to Sensation was first released in 2006. To say that it's a favorite doesn't begin to do it justice. Nalini Singh is one of my top favorite authors. I adore her writing. I love her characters. And even more amazing, I am absolutely enthralled with her worlds. 
 Over the years I've moved away from reading primarily Romance novels (usually fantasy/paranormal based) to reading more Urban Fantasy, Fantasy, and Sci-Fi. Though I love my happy endings, the sickly-sweet or too-erotic turn that most of romance has taken lately just leaves me ... apathetic. I've always said that characters are my first and foremost, and I still believe that, however, just behind character is world. I need the world to be intriguing, deep, and feel almost like some place that I could visit, someplace that could be real, in a slightly different time and place; maybe even in a parallel universe. 
 This is what Nalini Singh gives me, time and time again. 
 Don't misunderstand, this 
 is 
 a Romance, with a capital-R. And it has the 'instinctive-mate' thing going on, which is only half a step away from 'fated-mate.' Looking at the timeline I'm forced to admit that the romance develops quickly, however it doesn't feel like it's too fast. It feels like Lucas and Sascha take the time to get to know one another, that they understand each other, and that they genuinely like one another. The crucible in which they come together serves to heighten the emotions, quicken the pace of their romance, but I never doubt that they are good together. They belong together, and whether they came to that conclusion in a couple of days, weeks, or months, I believe in them as a couple. The 'mate' instinct is there for Lucas (though it doesn't really come into play until more than halfway through the book), but it's not what decides their interest in one another. It doesn't drive them to be with the other, only serves to reinforce the fact that he loves her and always will. And that makes my romantic heart sigh in happiness. 
 None of that would matter so much if I didn't connect with the characters - and I won't even get into the plethora of characters that populate this world because I'll end up talking about them in their own books, except to mention a couple: Hawke, Judd, Mercy, and Indigo immediately intrigued me. But it's Lucas and Sascha that drive this story. Lucas' need for the truth, his need to avenge his Pack, and his need to protect those he loves and is responsible for. It's hard to find fault with an Alpha that's everything an Alpha should be. Is he sometimes autocratic? Sure, but he also answers to his Pack, and to his mate. There's no decision that he makes that isn't open for discussion with his trusted advisors - who will call him on it if they think he's doing something wrong, because they're strong and awesome, too - and that makes him even stronger that the despots that many 'Alphas' become in other novels and series. 
 Sascha. Often in hetero-romance novels I've connected and been more interested in the male half of the couple, but here it was Sascha that I connected to most deeply. Without getting into spoiler territory too far (I know there are some of you out there that haven't read this series yet) I'll say that her psy-talent is one that I find incredibly relate-able. I love everything about her. But most especially, I love how her emotions make her strong. I love that she's independent and able, that she can take care of herself. That she's curious about the world around her. 
 This is already long, but I can't end it without talking about the world that has intrigued me for nearly a decade. Nalini Singh has created a world on the brink of revolution. The Psy, cerebral, intelligent, incredibly powerful gifts of the mind (including telekinesis, telepathy, and foresight - and many more that come up over the series), are without emotion. They feel no rage, no jealousy, no pain. There's no joy or happiness or love in their lives either. But they rule the world. And the Psy Council works hard to ensure that remains the case - no matter what lies they have to tell. 
 But no matter what the Psy think, the Changelings - those that can shift shape between animal and human (including wolves and leopards) - are not content to let the Psy run roughshod over them. They're not the 'dumb animals' that the Psy often relegate them to, and the world is changing. No longer can the Psy assume that they're the most powerful beings on the planet. 
 There are also humans in the mix in this world, and I'll only say that they don't come into play a lot in this book, but do later in the series. This world, the characters in it, and the story itself continue to evolve and become ever deeper as we continue through the series. And I love that. I also really, really, really love that there's such amazing internal consistency that I can trust every single thing said, hinted at, and revealed. On many of my re-reads, I've caught hints of events, characters, or story foreshadowing that still amaze me. 
 After a 100-years of this status-quo, we're thrust into this world and in Slave to Sensation we see the very beginnings of the evolution that is about to happen. Over the course of the next fourteen books the change is realistic, believable, and consuming. I've become incredibly invested in the characters and the world they live in. It's not an easy thing to change the world, and I continue to be absolutely enthralled with how Nalini Singh shows it to be done in this Psy-Changeling series. 
 This review is also available at The Book Eaters 
 Previous thoughts: 
 I love this series, and whenever I go to re-read it it's like falling into a familiar friend's embrace. It just makes me comfortable and happy and full of love. 
 The world is fascinating and incredibly well-thought out. It's detailed, yet easy to understand, complicated and diverse. The plotting (though-out the series really) is intricate and perfect. I've yet to notice a single mistake, continuity error, or something that pulls me out of the story/world. Impressive, especially now that we're nearly 12 books in. 
 And the romance. *sigh* Yes, there's a the "mate" trope. And yes, it happens rather quickly. But I never doubted their feelings for each other - or why they were having them. What I really like about Nalini Singh's matings is that even if they do feel the mating pull of their animal it's then backed up with actual real emotions, care and feelings. There're reasons they fall in love with each other - it's not just some fantastical fated thing. 
 This is one of the top 5 series I recommend to nearly everyone.