What sorts of information should be included in letters of recommendation?
The best letters are from faculty members (and others) who know you well enough to comment in some depth not only on your academic performance, but also on your personal qualities for a career in medicine. Both things are equally important! They should mention how long they have known you and in what capacity, and how well they know you. They should also put their remarks about you into some kind of comparative context with others for whom they have written letters.