I can remember watching Mister Rogers on TV a bit when I was younger, but only through reruns (I'm a child of the '90s), and not very regularly. Until recently, he was a faint memory in the back of my mind. He comes up now and again when there are terrible events (as the article mentions), but I wouldn't say he was a defining figure in my early development.
After seeing the movie, I can only wish that I had had more of him and his show in my life. He was truly dedicated to producing emotionally educational television for children. I think we could do with more of that these days. Children's shows just aren't what they used to be.
I think I'd give the biography a 9 out of 10. Not because it's some incredible feat of cinematic achievement, but because the message is so crucially important. Do yourself a favor and go see it.