1. I think BYU provides an exceptional education. I can not think of a school that provides a better education.
2. The quality of the student body at BYU is exceptional. I would say you will not find a group more overall ready for college than at BYU.
3. BYU overall is viewed highly by other schools for graduate education.

But there are some problems:
1. BYU does not get full respect it deserves for the quality of it's graduates.
2. BYU is competitive, meaning it is difficult to perform well and achieve high grades because you compete against many other exceptional students. Students who take college serious when they get away from mom and dad.
3. Schools that are more difficult to get into and viewed as equally or more prestigious than BYU such as Ivy league schools, private schools such as Stanford, USC, Rice, Tulane, Vanderbilt and others, and state schools such as UCLA, Texas, Michigan, Ohio State and others have graduates that get more respect than BYU grads and these are actually schools that are easier to achieve high grades because the student body as a whole are not as good of students as they are at BYU.
4. Because BYU produces such excellent graduates a disproportionate number go off to graduate education, causing schools to get overwelmed by BYU grad applicants forcing them to not evaluate all the applications.
5. These problems above are compounded by the fact that BYU students are catagorized as "not diverse" and given less opportunities for graduate education than they warrant based upon standardized test scores and class rank/GPA.

Because of these reasons I think many BYU students who do not get into graduate programs or professional schools of their choice would have had a much better chance had they put forth the same effort at other institutions.