How invulnerable is Superman?

As a sequel to my discussion of Superman's speed, how invulnerable to harm is the Man of Steel?
When Superman began in 1938, bullets did bounce off him, but it appears he was vulnerable to big explosions as "nothing less than a bursting shell could penetrate his skin."
By the 1960s, Superman was laughing at atomic explosions.
Enter the 1970s, where the only 4 weaknesses Superman had were Kryptonite, red sun energy, other things from Krypton, or magic.
Any weapon without one of those components did not affect the Man of Steel.
He could also fly in outer space without oxygen.
When Superman was revamped in 1986, he could be stunned by big explosions and was vulnerable to a lack of air. He was lucky to survive nuclear blasts and many alien weapons could affect him.
The reasoning now is that Superman is only invulnerable to most earthly things — bullets, fire and ordinary explosions. If something is hot enough, like a sun, it can fry him. His invulnerability is only relative to earth.
The problem I have is that in too many stories, he fights villains who clearly have no invulnerability and yet fight equal to Superman.
I also think that only magic, red suns, things from Krypton,including Kryptonite should comprise his weaknesses.
What do other Man of Steel fans think?