For me it was, A Ghoul's Guide to Love and Murder by Victoria Laurie There was this huge build up and then everything was wrapped up in two pages... what? Sigh... worse, it was the end of the series. I loved the edginess of the series and the female protagonist didn't get stronger or imbued with supernatural anything. She used experience and her brains (and the help of her friends) to survive. The ending was just such a cop out - "I'm married and pregnant, so I'm leaving. Bye!"
What about you? What was the last book you read and loved, but hated the ending?