I'll tell you straight away that Numbers was not a book I really 'connected' with. It wasn't really because of the characters - I loved Spider and thought Jem was a fine narrator. It was more that... I felt there was something missing from the story.
I love the concept of Numbers - that a girl has the curse (or gift) of seeing the date of everyone's death when she looks in their eyes. The story in the book, however, is pretty much just about two teens running away from the cops; the 'numbers' hardly play a role.
One thing that peeved me a bit: Jem is adamant about not telling anybody their number - to have to deal with knowing the day you will die is a burden and I agree with that decision, but when she sees people who's numbers are the present day, why not warn them!? Maybe a mere 'be careful today' from a stranger would be enough to save a life, but Jem doesn't even consider doing this.
In the middle of the book the plot got slow, and I mean really slow. It took a bit of effort to get through. The ending is expected, but a surprise at the same time. It opens the book up for its sequel, which isn't something I plan on buying.