Believe it or not, Jack Kirby didn't shit rainbows and lactate wonder. A very good artist, professional, and seemingly a wonderful guy, but come on: he did Dingbats of Danger Street. It's pretty clear that his work on the legendary run on FF was only helped by the presence of Stan Lee to help rein the guys more elaborate fancies in. This isn't to say I don't love the idea of a small planet of vampires and other monsters in Dabney Donovan's basement, much less the idea of Superman fixing everything by playing the film version of Oklahoma at it. But take Darkseid, for example. Since Darkseid is basically a god of pure fascism, it's difficult for most writers to avoid failing to actually use him effectively in a story. The best stories involving Darkseid outside of Kirby's work are ones where Darkseid actually acts, which is rare: the best non Kirby Darkseid story for my money is stil The Great Darkness Saga because (gasp) Darkseid is an active force of evil and menace throughout the story! He does things! He turns an entire planet into a bust of his head just to be a dick! Compare this to "Legends" where Darkseid's evil plan involves daytime talk television. I realize I'm blaming Kirby for what people did with his creations here, but it's not Kirby's fault, it's the fault of the ridiculous fetishization of his work. Still, Darkseid's a less compelling villain than half of the ones ripping him off, because they at least get to go around doing evil things. Darkseid gets to sit around and talk to Desaad.
You do have to give Kirby credit for understanding that the Marquis De Sade was pretty up front about tyranny and how he'd go about it. So many writers just use Desaad as a sniveling henchman and toady, but Kirby always depicted the relationship between the two much more subtly. Desaad is often the only one willing to tell Darkseid off. Admittedly, he usually ends up paying for it. "Once upon the throne of kings" and all that. I wish other writers could grasp that complicated relationship: when Paul Levitz managed to have Darkseid actually miss Desaad, he got the point of what Desaad does for the figure of Darkseid as an evil force. (Then again I hail from a country where people are totally okay with torture so maybe I expect too much.)
Please, though, fuck the Eternals. It's not even that they're a bad idea, it's just that Marvel already has too many cosmic entities patterned after various mythological figures. The Eternals would work perfectly as a stand alone, doesn't interact with the Marvel comics in any way story/setting, but having Ikaris and Thor hang out is just too weird. Thor actually is a god! It's weird! Having the actual Greek gods running around in a setting with cosmic powered immortals who were thought to be the Greek gods is just storytelling hash, you end up with story after story trying to reconcile the two. And frankly, multiple stories (even ONE story) that are just excuses to explain minor points of comic book trivia aren't really compelling. I was surprised that I didn't hate Gaiman's Eternals more. (I honestly don't have any major complaints about it even. I was surprised too. I didn't like it, but it didn't actively enrage me.)
They used to call Marvel "The House of Ideas" but aside from Kirby, Ditko and a few others like Steranko it often seems like the only idea was "Wouldn't it be neat if the skies rained shit down on superheroes?" which, to be fair, was a fairly novel idea at the time. (I'm actually giving Ditko incredibly short shrift here, which is totally unfair of me, but bear along) - stories like Brave New Day bore and disappoint because they borrow heavily from the "Look at all the crap Peter Parker has to go through" without any of the "Lost city full of whacked out freaks" aspects of Marvel's Silver Age. What Marvel needs now is a passel of wildly creative types and a moderately clever guy with a real editorial flair to round them all up and make them produce good stuff without letting their egos out of check so that we don't get a year of Norman Osborne running the world.