There was a time in the late 1970's/early 1980's where John Byrne strode over the comic industry like a god.

He came to prominence with the Claremont/Byrne/Austin issues of X-MEN (issues 108,109, 111-143) from 1977-1981.

He also had memorable runs on:
AVENGERS (issues 181-191),
CAPTAIN AMERICA (issues 247-255),
IRON FIST (issues 1-15,
and
POWER MAN/IRON FIST 48-50),
among many others.

And his signature work, FANTASTIC FOUR 232-293, where he wrote, pencilled and inked the series (which is a great run up through issue 274) and his tour-de-force brought FF back to the heights of popularity. I would argue that it was during the last year and a half of Byrne's run on FF (issues 275-293) that he began to decline.

And although his MAN OF STEEL/SUPERMAN/ACTION COMICS/WORLD OF KRYPTON run from 1986-1988 was a period of renewed interest in Byrne for his significant changes in Superman's mythology, this also represented an even further decline in Byrne's art, despite some good writing.

From 1975-1982, Byrne's art got increasingly detailed and refined. And it seemed to me that he just stopped caring about his art sometime in 1983, and from that point forward over a period of years, his writing began to decline as well.
The first solid clue was when he announced in a letters page (FF 258) that he was drawing in ink, and skipping the pencil stage. I remember reading this and thinking that this guy no longer cares about his art.

But I still have fond memories of Byrne's early work, and occasionally have enjoyed some of his later work as well, such as his SENSATIONAL SHE-HULK run (1989, and 1991-1993)

I think Byrne's career breaks down into several different eras:

Early Period (Charleton) 1975-1976
Early Marvel period 1975-1980
Marvel, the Peak Years 1980-1986
DC/Superman period 1986-1988
Back at Marvel period 1989-1993
Dark Horse period 1992-1994
DC, Mid-1990's period 1995-1998
Marvel Again, Exploring Early Marvel period 1998-2001
Current DC period 2002-2003

I'm really curious why an artist who seemed so dedicated to the quality of his art, and was very popular and praised for that commitment, suddenly took such a shameless dive in quality and seems to have just stopped caring, despite being one of the highest-paid and most recognized artists in the field.
This is the same guy that in the early 1980's would rip on other artists like Gil Kane and Don Heck and Bob Layton for the slightest imperfection in their work, and in particular ripped on many Silver Age artists for "doing nothing" to advance their art. And then Byrne HIMSELF became the epitome of a hack who continues to churn out half-hearted work.

As hard as Byrne was on his fellow professionals, I think Byrne has gotten relatively little abuse for the drop in quality of his own work.

There was a time where Byrne's work just got better and better, and he was arguably on a par with greats like Starlin, Gulacy, Buckler, Romita Jr., Perez, Rogers, Grell, Brunner, Chaykin, Simonson, Day, Bissette, Tottleben, Golden, Miller, Giffen, Paul Smith, Art Adams, Brent Anderson and Bill Sienkiewicz.

And even approaching the level of Neal Adams, Berni Wrightson, Michael Kaluta, Barry Windsor-Smith, Frazetta and Corben.

But at some point Byrne just oddly stopped caring.

What went wrong?

And on a more positive note, what are some of your best-loved favorites by Byrne?