I'm not going to do a review proper because it already has a (16/16) review on MAL and I'm feeling lazy. Sorry!
Lament of the Lamb - 7-8/10
LotL is a gradual descent into the darkness of the mind. There are very few main characters, and most spend the majority of the series brooding. It's a compelling read because of the gloomy sense of hopelessness the series has. The cast reflect the situation by very rarely smiling. It's depressing to read, certainly, yet I always found myself wanting see what was around the corner, despite the often sluggish pacing.
Reading it, I couldn't help but be sucked in. When I first received the first five volumes way back, I started reading the opening volume at around 1 AM and stayed up until 6-7 AM to read through all I had. That's how much it absorbed me; pulled me into its bleak world.
The most fascinating aspect is, without a shadow of a doubt, the relationship shared between Chizuna and Kazuna; the brother and sister of a cursed 'vampire' lineage. They grew up not knowing each other, Chizuna suffering from her need to suck the blood of others from childhood, living off her father, and Kazuna living a relatively normal life. However, Kazuna's life all changes when he starts lusting for the blood of others and, after going back to his old family home, runs into his long lost sister. They start living together shortly after this - Kazuna seeing his mother in Chizuna and Chizuna seeing her father in Kazuna. Chizuna is best described as twisted, having had a love-hate relationship with her father because, after her mother's death, he started seeing her as the replacement for her mother due to her resembling her, and she depended on him for blood. With Kazuna in the picture and her father dead, the roles are reversed - he takes blood from her - but he still fulfills the role of being the replacement for her father, him resembling their father. It's hard to get a firm grasp on their relationship - they aren't brother and sister in actions, as them kissing highlights, but they also are not lovers.
What ultimately let the story down was its lethargic pacing and 180 ending. In the sixth volume in particular, too much time was spent on needless subplots. One subplot involved a character trying to uncover the truth behind the suicide of Chizuna and Kazuna's father, going over old ground and then vanishing. Although it did open the path to the big twist of the series, far too much time was spent with the 'camera' on this mostly pointless character. As for the ending, it came close to ruining the entire story; ending on an illogical high after all looked lost at the end of the next to final chapter. In short, if the story had been 'tighter' and chapter 47 hadn't occurred, it would've been a far more enjoyable story to read.
Worth reading? Yes - it's different enough to be worth the time of most - but it's far from perfectly executed.