I have seen a lot of people argue over whether Progressive Rock or Progressive Metal is better. So, to be a bit more interesting, I'm going to highlight a few things that can be found frequently within both genres.
Number 1: Concept Albums
The vast majority of Progressive artists have released at least one concept album. From Pink Floyd's fairly easy to understand classic "The Wall", to Tool's incredibly strange and unconventional "Lateralus," the concept album is a amazing, if almost annoyingly common sight among the discographies of Progressive Rock and Metal bands.
Number 2: Classically-Influenced Guitar Work
If you actually take the time to listen to the guitar in many Progressive songs, there's a very strong hint of Classical music. The key examples of this, at least in my opinion would be Yes' "Roundabout" and Coheed And Cambria's "Welcome Home," though there are quite a few that I could list, if I really felt like it.
Number 3: One-Word Band Names
Off the top of my head, here are a lot of Progressive Rock and Metal bands who have names consisting of a single word: Yes, Rush, Genesis, Kansas, Queensryche, Tool, Opeth, Mastodon, Buckethead, Deftones, Rainbow and that's just in five seconds of thinking.
Number 4: Anti-Egos
What I mean by this is that I've seen a good amount of interviews with musicians playing in bands who are considered Progressive and all in all, I can safely say they're some of the most mentally casual and stable people in the music business. Excluding Alex Lifeson's Rock And Roll Hall Of Fame speech.
Simple stuff to think about and as a conclusion, I would like to say that anyone reading this should feel free to post more similarities between Prog Rock and Prog Metal, in the comments below!