As an avid player of Vampire, a history major specializing in the ancient near east as an undergraduate, and now as a graduate student studying biblical studies, I was very excited when I got my hands on Jerusalem by Night. Jerusalem certainly is a great place to set a vampire game, and I thought this book would open up the door to a lot of ideas for a campaign.
However, the book is lacking in many key areas. Most specifically, the history section of the book, in which over 2000 years are summed up in a few dozen pages, is some of the most dry and uninspiring writing I have ever read in a white-wolf product. Concepts are sketchy at best, mostly glossed over, and of questionable accuracy. In addition, there is almost no attempt by the author to tie vampires into the history--only some feeble mentioning of vampiric activity that was misinterpreted as acts of God or the introduction of a character only to say that said character came to the city at this time. The vampires do not seem to manipulate Jerusalem as they do other cities.
Another complaint I have is the way in which the author defines the religious groups of mortals who live in the city without going into detail on any of them. We don't know who controls the groups, what they want, how they operate, etc. And some ways in which they are defined is not only incorrect, but offensive to those groups. Take, for example, the name by which the author refers to Jews. He routinely calls them "Followers of Yahweh". While technically that may be correct (as God's name is given as Yahweh in the Torah/Old Testament), Jews are forbidden to use the name of God in speech and would refer to him only as God (in Hebrew: Elohim) or Lord (Hebrew: Adonai). If they were reading God's name, they would say only "The Name" (Hebrew: ha-Shem). When referring to them, you should say Hebrews, Israelites, Children of Israel, or Jews, depending on when in their history you are referring.
My final complaint is that in one of the oldest cities in the world, the author does nothing with the myriad of possibilities tying vampires to the religious world. I am not sure if he was afraid to offend or if he just lacks true vision of what could have been.
All in all, this book takes what could have been a great concept for a campaign and does not do anything with it. It is dry and inaccurate, and doesn't really give you too much to work with. The only value I see in it is that it does give you some non-player characters to steal for your game, but that is not enough to make it worth it. Do yourself a favor, if you want to run a game in medieval Jerusalem, go and by a basic history book on the city and make up your own stuff about the vampires who populate it. Your money will be much better spent.