There actually isn't that much in the way of metal influence on the sound to be honest.
On the album Amino Acid Flashback, there was only one song with metal riffing and clear metal influence and even then it didn't make up a majority of the song. When you put on OHM: you really need to listen to jazz fusion ears, because if you're expecting to hear a fair bit of metal in there you'll just be disappointed.
If you can look past that aspect, IMO all 3 OHM: albums are the greatest achievements in jazz fusion this decade IMO.