There has never been a rock vocalist like Bon Scott, before or since his death. Because of the style he used in AD/DC, people do not realize the guy was actually technically a very good singer. There is some video of some of the Australian bands Bon played in before AC/DC, including a folk rock band which showcases Bon's quite good singing voice.
Another thing most people don't realize: Powerage is the best AC/DC album by a country mile, and I actually rank it in the top five rock albums of all time without hesitation. When you get right down to it, those first five AC/DC albums with Bon Scott set the standard for their style, totally revolutionized how people ultimately came to consider good hard rock, and as a body of work they totally blew away the Brian Johnson era -- even as good as the album Back in Black was. And I actually like Brian Johnson.
Just my two cents.