I grabbed this book because of the references I saw some friends make, likening it to Kresley Cole's Immortals After Dark series. Unfortunately, I think that comparison may have dimmed my enjoyment of The Darkest Day a bit. 
 My favorite thing about this book is the premise the world is built on. Humans have actually died out, fairly recently - last quarter century or so - and immortals are the only beings left living on the Earth. I think that's a fascinating concept, interesting, new and fresh. Immortals still have some human blood, so characteristics aren't uncommon yet, but the fact that there aren't humans around immediately drew me in. 
 Beyond that, though, everything felt like fairly standard fare. It didn't make me think too much, or feel too much, or become completely invested in the fates of the characters. Izel and Kelvin were pretty much like any other paranormal hero and heroine I've read. Izel is a female that's surrounded by stronger males, her choices removed from her and forced to travel with the moody temperamental immortal male. Kelvin acts as a pretty typical shifter - though he can't actually shift - possessive, territorial, demanding. He's also incredibly angry, and often cruel, because he is so desperately attracted to Izel. 
 Occasionally Izel strayed into too-stupid-to-live territory, which was frustrating. Having spent the majority of her life without feelings, and then being overrun by them made it slightly more understandable, but running off into the wilderness knowing that other beings are going to scent and hunt you makes no sense to me. Also, though she grew up in this world as an immortal she knew nothing about any of the other species populating the world with her. Kelvin had to explain everything, and keep her safe from herself. 
 All of that didn't prevent the sexual tension between the two from fairly steaming off the pages though! I thought there were a few times that I was going to melt from the heat between them. This is probably the strongest part of the book. I absolutely believed in the sexual need and desire between them, even when I never understood why they fell in love, except for them being fated mates and all. I actually like fated mate stories, if I see them falling in love with each other as part of the story. 
 All in all, The Darkest Day was a good read with hot tension filling it up. I think if I hadn't been looking forward to something intricately plotted and paced this would have satisfied a great deal more. The writing was fairly strong - though the faux-Scottish brogue did get on my nerves more than once - and I will definitely be willing to check out more by Britt Bury in the future. 
 *** 
 Original Thoughts: (view spoiler)[2.75 Stars I think. 
 Full review to come. 
 The book was pretty well written, the world had the potential to be interesting, but the dissapointing thing, for me, was the relationship between the hero and heroine which was all lust, angst over the lust, and fated mates without me ever really figuring out why they fell in love with each other. 
 Decent way to spend my time, and I'll probably check out the next one, depending on who it's about. (hide spoiler)]