Top Ten Things that a Metal Song May Have to Make It Unique

Thrash Metal songs have a lot of good guitar riffs, mostly the fast shredding, but others like the ones you find in Blackened by Metallica may be slower but are harder to play.

Metal riffs are so amazing that very often I listen to some metal songs for their riffs, even when I don't like some other things in these songs.

Usually this is a good thing, as it makes the song exciting. However, a few genres like Doom Metal are better off being slow, but uses dark rhythms and horror themes in lyrics to make the songs heavy.

I prefer very fast metal songs. This is a huge part of the excitement. Metal is the fastest music genre in existence.

Fast metal songs are basically about anger, hatred etc. Slow metal songs is basically about sadness, emotion etc.

Sometimes speed can be a bad thing...

Yes, one of the reasons I love metal. Great vocals make metal songs stand out - singing voices with power, range, emotion, real vocal skills and endurance. Especially power metal singers.

This is something you'll find a lot of in Power Metal bands like Blind Guardian. In Thrash Metal and Death Metal, it's mostly screaming, but enjoyable.

Yes, some metal songs are known for their drumming. Metal drumming is awesome, I love especially the double bass.

Example: Dyers Eve - Metallica. The only song where Lars Ulrich did an extremely good job drumming.
Painkiller - Judas Priest. Known for the drum solo at the beginning of the song.

The intro drumming of Where the Rain Grows by Helloween and Run To The Hills - Iron Maiden for example.

Lyrics can be about anything, but they have to be strong

Most Metal songs have good meaningful lyrics, mainly about politics, religion, or struggles. There are so many of these songs, but here are some examples:
Metallica - The Frayed Ends of Sanity
Cannibal Corpse - Hammer Smashed Face
Dio - Rainbow In The Dark

See my post on the heaviest metal bands for further info about this.

True. I like metal songs for it. Especially progressive metal.

Yes, metal songs tend to have progressive structures: bridges, pre-choruses, time signature changes, tempo changes, drum beat changes, switching from clean to screaming/growling vocals, etc. This makes metal songs less repetitive and less monotonous.

High-pitched screaming is great. Rob Halford for example.

This is better in Thrash and Death metal.

Bass solos make a song more unique. Not only in metal but for all genres. A bassists can do almost everything that a guitarist does. In some cases, a bassists can do more unique things. Cliff Burton for example.

Bass solo are awesome.

Example 1: Hangar 18 (Megadeth) - This song has 11 guitar solos, but nothing important for the bass or drums.

Example 2: Metropolis Pt. 1 (Dream Theater) - This song has some solos, but at least one for each instrument played.

Example: Hells Bells (AC/DC) I know this isn't a metal song, but still. The bells you hear at the beginning and are played throughout the intro riff make this song unique. Metallica did the same thing with For Whom The Bell Tolls, but that song was released afterwards which does NOT make the song special in any way.