Ever take a trip back to find music that help define "heavy metal"? This can be a journey that gives us memories of our days gone by and a chance to discover music that we're not all that familiar with.
I came across a post on guitarworld.com that has 20 heavy songs that may be on a playlist or two of yours. If not, you might consider adding them.
Here's the link to the post: 20 Heavy Songs Before Black Sabbath