What do you need to know? Most students board, they have a large endowment, their admissions are rigorous, easier if you're the child of an alumni, or you know somebody... Programs are good. It wasn't on our short list however... we were looking at Middlesex Academy in Concord or BU Academy for our DS, but ultimately chose a different path... but we spoke to many people who had a plethora of information about a lot of schools.... you might also want to look at St. Paul's, which is a boarding school near Concord NH, extremely rigorous to get into no matter who you know... there is a DIS'er or two who went to Philip's Andover, so perhaps they will chime in....
I just noticed you are in California, you might also want to look at Groton School in Groton MA, it's an extremely rigorous course, although recent administration is of questionable moral ethics, it is still a top notch school. DS would have been applying for admissions for next year had we not changed direction. He's coming for a preparatory education, so we have a bit of experience with all of the prep schools in the area.