Run No More by Catherine Mulvany.
I'll be honest that I loved the story from the beginning, it was intriguing, the setup was interesting, and it had a mystical element mixed with crime and espionage that sparked my interest. I liked the relationships between the two main characters. However, almost towards the end at one of the pivotal moments of the story, there was a horribly written sex scene. I didn't even finish reading the book it was so awkward, it took me out of the story completely and I haven't picked it up since. That was a huge disappointment because I was really enjoying the story up until that point. This goes back to the discussion about contrived romances as a least favorite plot device, or rather in this case authors who simply cannot write romance scenes to save their lives and end up cheapening the story that actually had potential of going somewhere good. I find this happens a lot in certain cases, authors need to focus on their stronger points in writing, sometimes sex scenes shouldn't be written to say that hey, two characters are being intimate with one another.
Another one isn't much of a disappointment, but more something I just couldn't get into: the Kushiel series by Jacqueline Carey. They are a really good series, I am certainly not denying that at all, but the writing style just didn't pull me in. I guess I'm more disappointed in myself that I couldn't get into it like I thought I would, since it was recommended to me. Those kinds of fantasy-style books just aren't for me, I suppose.