Start with the easy part! Monsters of New Haven High - last update 4/02
Why? Because it is bloody well written? 
It lets you play a full on monster or a reluctant one, a traditional or rebellious one. But still human enough to be able to relate.
Doubt I could pull off playing Cthulhu, or an utterly alien race (look to Traveller - tabletop RPG - for alien races!) - I do need my colligated foothold. 
Now, Choice of the Vampire - I don’t much like vampires, but the game is so well written it drew me right in. So, uh, I suppose for me that is what it comes down to - a well written game. Now, I would not read a book about vampires, due to lack of interaction, in part from not caring much for vampires (except the classic old BW Dracula style vampire who at best can fake humanity poorly - no neo-goth emo-woe-is-me undead-life-is-so-hard vampires, please - just go out in the bloody sun if it is that hard, geez…).
Er… Side-tracked. Oops. 