Some positives that I remember:
Lack of stress over back-to-school clothes shopping: uniforms took care of that and were a lot cheaper overall.
Love of the Mass and Catholic culture: honestly, that was the biggest thing I took away.
A solid emphasis on education: I was well prepared to be successful in high school after my Catholic elementary education.
Respect for diversity without it being forced: our school accepted non-Catholic students, and as such we had students who were Catholic, Protestant, E.Orthodox, Hindu, and Muslim from a number of ethnic backgrounds. We all learned by interaction with each other and by the examples set by the faculty and staff to respect each other as human beings. In the entire time that I was in Catholic school, I don’t ever remember hearing a racial, ethnic, or religious slur from anyone.