I've never developed any affection for metal, but bear in mind that I grew up in the 80s when it was so popular that you didn't have to be good at metal to sell albums - you just had to buy a guitar and a wig and learn to twitch rhythmically. So it's possible that I was inundated with bands who are better off lost to history, drowning out the actual talent through sheer volume.
Some of how I consider the difference between metal vs rock and pop.
Time signature: rock will almost invariably be 4/4. It's the easiest time signature for the listener to follow along with. Expanding slightly, a lot of elements will follow a predictable pattern of being 4, 8 or 16 measures long. You'll find a lot of metal songs with 4/4 timing, but you'll find plenty using other time signatures. Also if you listen closely to the drums, metal songs tend to be faster. Rock songs do some things to sound faster, but the kick drum is the telltale.
Sound style: a lot of hard rock, hair metal and nu-metal borrow heavily from the sounds of metal. Really this is just picking which kind of effects and where you're turning the knobs. I can put Mozart through the same filtering process, doesn't make it metal.
Composition: Listen to a song by Def Leppard and Linking Park, pretty much any song from either band will work. Then listen to most (not all) songs by metal bands, I'll pick Ride the Lightning from Metallica, not their most iconic, but still representative.
The DL or LP song if you pay attention, you'll notice the guitars almost disappear during the verse. They're still there, but either very subdued, or playing single notes to accompany the vocals. When the refrain or chorus comes though, the instruments play their more aggressive parts. It's louder and really pushes the vocals louder at the same time. This is the part that usually has the most memorable lyrics, the part where people are most likely to sing along.
Ride the Lightning the guitars keep a fairly constant state of volume and presence in the song. During the solo obviously one guitar takes prominence, but that's what a solo is. Guitars are much more prominent and heavy handed in metal vs rock or pop.
There are other characteristics I look at, but they're less universal and more indicative of good or great metal bands, instead of the genre as a whole.
Funny we wrote in 2/4, 4/2, 3/4, 6/8, 7/8, and yes some mixed 4/4, with 3/4 etc. Dream Theater and other Prog Metal does this a lot. They break away from the Bon Jovi, Motley Crue, Poison 4/4
One of the first riffs I wrote was 7/8 took me YEARS to find a drummer that could handle it and know what to do with it. Funny that drummer was one I worked with long before that and he could not grasp it, then one day after we had started working together again he got it. I was asked SO many times how do you do you play that riff. I would never tell. I actually used that riff variation in a lot of stuff I was writing when I left the band.
The song was done in drop D on the 6th string and then 7/8 timing. it was very dark and very fast without being speed metal or thrash. It was pure on Prog.
Last time I picked up a guitar I remembered how to play it but my chops were so off I wanted to cry. I miss playing in bands
Metal bands are much more likely to use alternate time signatures, prog bands even more so.
The verse-chorus-verse-chorus with a 4/4 time signature makes music really accessible for non-musicians. It's why pop music doesn't deviate from it much (a few do, but not often and not many). It's why I consider hard rock, hair metal and nu-metal to really just be harder sounding pop genres. Not that that's a bad thing, I like at least one band, if not more, out of each genre, but it's one of the ways I've found that helps me differentiate between them.
I miss playing as well. I was never very good though. I also played cello for 6 years, wasn't very good at that either.