Someone on a Slack posted a
recent Megadeth live performance in which Marty Friedman joined them. (Both the very first riff with the harmonics and the start of the Marty's solo sound off, but that's beside the point.)
He mentioned So Far So Good…So What?, and it just occurred to me how that album is still striking in that it this really unhappy vibe that's still kind of unsettling. Not unhappy in the metal lyrical topic sense, but when I heard it, even for the first time, there's this underlying feeling that there's something wrong with the people playing the music.
For me, neither Peace Sells nor Rust in Peace create that sense — no matter how dark things are melodically or lyrically, there's an exuberance and brightness driving it. Everything in So Far So Good…So What? is on time and very technical, but has this "dying smoker" vibe.