The results of the BGO report to the board are not revealed to the candidate UNLESS your BGO lets you know. Odds are, if you showed interests (i.e. you have done some research on USNA, have an interest in a military career, being a leader, not selfish/arrogant, etc.) and you can demonstrate reasonably (notice reasonably...doesn't have to be perfect) in an interview (in which you dressed for the occasion), you probably are going to get some type of positive report (how positive is difficult to say). If you can honestly fit yourself into the description above, I wouldn't lose sleep over it....BGO interviews tend to fill gaps in your application...in other words, something that your application data might not reveal or something from your application that could be amplified (and would not have already be known to the Admissions Board).
My interviews tend to go about 2.5-3 hours, so what yrangd experienced isn't abnormal. Each BGO is suppose to conduct the interview in a particular way, but they might not be "exactly" the same.