Yes, I was very pleased with elementary school in Japan for all of my 3 kids. However, middle school assigns no homework and is teaching my son nothing. Without juku, an extra cost of several 10000 yen per month, my kids would have been screwed. Via juku, my kids raised their dispersion score - hensachi - by about 20 points. So in my view, Japan FAILS obligatory education - gimu kyoiku - at the middle school level and allows private educators, i.e. juku, to fill the gap. This sucks too.
OTOH, my first son's private high school was excellent, and my daughter's public high school was also excellent.
So maybe the failing is middle school only.