I think it still holds up and is worthy of its status as a classic.
In many ways it solidified the idea of Superman, Batman AND Wonder Woman as the three pillars of DC. They'd interacted plenty of times before then, and Wonder Woman has been one of the biggest icons for decades, but
Kingdom Come was one of the first--if not the first--to really present them as the TRINITY.
It also, in my opinion, presented an interesting take on Diana by exploring what she would be and do if she lost faith in herself and gave up on her belief in peace. That's kind of the critical thing with her in
Kingdom Come: this is a Wonder Woman who believes she's failed and is overcompensating by turning into a fatalistic zealot. Diana dressing in full battle armor and waving a sword around in this story is a Diana who's given up on herself, and that's not a good thing.
The issue with
Kingdom Come...as with many seminal works...is a lot of creators take the wrong lessons from it, and that has had a negative impact on Wonder Woman (and maybe the DC universe as a whole). Too many looked read this story and took away: "Wonder Woman with a sword is bad-ass!"
Not necessarily a bad thing it itself, but give it a few years, and we end up with the worst of the New 52 where Diana brags about chopping heads off and needs to be
told to protect civilians during a battle.
But like I said,
Kingdom Come itself still holds up despite some flaws (the conclusion to Wonder Woman's arc isn't conveyed as well as it should). Even if many fans and creators took the wrong lessons from it, and we're still feeling that impact to this day, I try not to let it diminish my appreciation for the original story.
For anyone interest, I go into greater detail on
Kingdom Come and its impact on Wonder Woman here:
https://talkingtothevoid.blogspot.co...der-woman.html