River City Ransom is awesome, but my favorite Kunio-kun game on the NES is Super Dodge Ball.
Mega Man 3 is probably my favorite of the classic NES ones. Start with Top Man's stage, he's the easiest.
The cutscenes in Ninja Gaiden were pretty revolutionary back then because before then, not many games told the story between levels. It was all done in the instructions. But man alive is that game hard!
One of my unpopular opinions is that I like Mario 2 more than 3. 3 is still great, but for some reason, I just always enjoyed 2 more.
I've heard about those Frog Detective games before. I would love to review them.