I enjoy most of Moore's current work -- Tom Strong, Promethea, Top Ten, League of Extraordinary Gentlemen -- but in many ways, these older tales have a power and a poetry that those more recent works don't attain. I've never felt the impulse to read, say, Tom Strong aloud -- and I can seldom resist the impulse to do so with Moore's Swamp Thing.
Yes, Moore was at his wordiest in those early tales, and it could be argued that the more economical prose of his current work shows a more "sophisticated" touch, that Moore-The-Wordsmith has learned to integrate more of the visual aspects of the medium, and so on, and so forth, warming the heart of Scott McCloud.
Be that as it may -- those stories were compelling. Moore's "America's Best Comics" are merely... amusing
And one of the things that makes them compelling?
Moore's use of "continuity", of established characters and the oft-maligned conceit that all these characters co-exist in a single weird and wonderful world. Swamp Thing himself, of course, was a character with a well-established background who'd gone pretty much nowhere before that upstart Brit took the reins. Moore didn't just let his mossy protagonist and his supporting cast exist in a vacuum, however. Those issues were probably the most "crossover"-heavy in the character's history, before or since: a Batman villain provides the key to the mystery of the character's origins. The Justice League of America has a masterful cameo. Other "supernatural" DC characters have more significant roles: Etrigan the Demon, Deadman, The Phantom Stranger, The Spectre. Moore even dredged up the genially creepy hosts of DC's long-defunt "mystery" anthologies and recast them in an entirely different light.
These were not throw-away tie-ins. They were integral to the storylines. It is hard to imagine the scenes having the same impact if Moore had substituted "generic" equivalents to fill the roles (though he would demonstrate that he had mastered that trick, as well, in 1987's Watchmen). Nonetheless, one can read them without feeling lost simply because one didn't know the 40-year history of each particular character. They are self-contained, but nevertheless draw from a realized world.
Continuity and "Universes" have fallen out of fashion with those who style themselves "sophisticated" afficianados of the medium. A few years after Moore left the book, the character became one of the flagship titles of the "Vertigo" imprint: serious, "mature" comics, largely with a modern fantasy/horror theme. The Vertigo titles were set aside from the "DC Universe" -- it was felt that crossovers with brightly-clad superhumans detracted from the dark, moody theme of the line.
The Swamp Thing stories of that period can charitably be described as "forgettable". Certainly, it yielded nothing as powerful as "The Anatomy Lesson" or "The Brimstone Ballet". Emphasizing the style Moore set lost the substance of his work.
Of course, Alan Moore is a damned hard act to follow.