I would recommend talking to as many people in the field as you can. I was interested in forensic work at one point, and have completed a few forensic evaluations (risk assessments, competency to stand trial, parental fitness, and psychosexual evals) during my practicum and internship training. I think it is interesting work, and there are plenty of jobs out there. I chose not to do the work as I like doing treatment a bit more, and don't like the adversarial nature or how the legal system handles mental illness. I will say that I know several psychologists who are happy with the work, and make good money. Sex offender work, in particular, seems to be in high demand (both assessment and treatment). I found "Getting Started in Forensic Psychology Practice" by Eric Mart to be a pretty good intro into the work that forensic psychologists typically do, but the best thing to do is to talk to as many people in the field as you can, and get a mentor.