We were nervous about sending our kid to Rosemary Hills, but we had a good experience there and were glad we did that instead of private.
I found the best things about Rosemary Hills were the teacher and the parent community. With such a large school, if 1 in 10 parents volunteers, then you have a good pool of volunteers, and everyone seems very committed to making sure kids have a good start to school. Out of three years, we had 2 very good teachers and one ok teacher (who I think is no longer teaching there).
At CCES we again have also been happy with the teachers, but we're still there. They have a good instrumental music program that starts in 4th grade.
Personally I think class size is the biggest difference that private school can offer over public school, and/so I think sometimes its importance is over-stated.