(This post is concerned only with American comics. Please read with that in mind. Thank you
There's no doubt that Watchmen is amongst the most influential comics ever written, and that it and DKR are widely regarded as the main cause of the 'realist movement' in comics.
Moore himself has often stated he deeply regrets that other writers read his work and then copied him rather than being original themselves in their own approach.
There's also no doubt whatsoever that most writers who have followed have entirely missed the point of what Moore did - which is to say, if you want 'realistic' you have to make some really serious changes to the world to reflect the presence of all that super-science and all those ultra-powerful beings. Trying to pretend a world so very nearly our own is 'realistic' because you add a thin veneer of Grim N Gritty is embarassingly absurd.
Truth is, you either write 'realistic' - with all the consequences that that implies - or you don't. There's no half way house.
The traditional approach to superheroes is the nod and the wink to the readers. We all know these larger than life people who never have a bad hair day let alone give up against insurmountable odds or - horror of horrors! - actually lose
are totally unrealistic on any level you care to name, but that's never been the point of them. Superheroes are meant to be fantastic, aspirational figures who are far larger than life and whose deeds are the stuff of legend.
If powers really went to 'ordinary people', most of them would be used to impress their friends and interest members of the opposite sex, and that would be it. That's 'realistic'. Almost no-one would go out to save or conquer the world, and both 'heroes' and 'villains' would probably be certifiable. That may work as satire, but it's nothing I'd want to read taken seriously, and certainly not in any of the adventures of my favourite superhero characters.
Superheroes are unrealistic. They are, their world is. That's how the genre works, and that's how we like 'em.
Is Watchmen truly to blame though? I think not. The problem is that a lot of lesser writers jumped on a bandwagon that Moore never wanted to start in the first place, and that's hardly his fault.
On the other hand, without the darkening of comics we'd not have gotten an awful lot of good stories, including most of the stuff written by Garth Ennis, to name but one. I'd consider that a huge loss, and I'm sure others would, too.
Truth is, comics should not ever return to being written solely for small children and only allowing for light and happy stories. The medium is capable of so much more, as the Vertigo line has so often proved. What is needed is for a rebalancing of the scales: a recognition that comics are as much a valid medium for storytelling as novels or films. And that there is nothing wrong with writing superheroes as
superheroes, and within the classic tropes of the genre.