From the alien Krypton to Clark having to win Lois' heart AS Clark and not as Superman, to the relationship between Clark and his parents and Lois and her parents, and Luthor and Lois and Luthor and Clark, Perry and Luthor, etc.
Byrne's comics were character driven instead of plot driven like what had been done till then and is being done now.
Today the plot dictates what a comic is going to be about, the characters have been lost because people like KK and Mxy have spent the last few years complaining that Superman has been talking with his parents more often than he punches someone on the head.
What Byrne did was offer a more grounded perspective to the character and this brought forth many character-driven stories and moments.
Along the way he introduced new elements, like the afortmentioned alien Krypton, (with Wolfman's help and inspiration) an egomaniac Lex Luthor who hates Superman for being more popular than him (instead of hating him for burning his head), stuff like that.
When it comes to character Byrne's comics win over the crap we've been subjected to since 99...
I mean, Superman vs Dracula... what the fuck was that about?
Once a hero fights Dracula it's clear that the writer has run out of ideas...
Comics are like a Rorschach test; everyone has a different opinion on what they are and can be...
