Yup, a totally real universe parallel to our own and by hal's own power. In fact there were incalculable number of universes created by rookie lanterns. A seasoned lantern like Sinestro was supposed to control all of them by himself though.
Only a bitter little adolescent boy would confuse realism with pessimism
Captain Atom from DC. Legion from Marvel(he's a high herald level character at average portrayals).
Though these types of feats should not really be applicable since the herald in question is tapping into a greater external power source(except for Legion, who's simply unlocking a new powerset when he performs such a feat).
The Hal universe creation showing is not valid since it's written by Dematteis. Sometimes to understand the comic you have to understand the writer. Dematteis believes in Hinduism: that all reality is an illusion. As such he believes that every human is capable of creating their own private realities, which are no less "real" or tangible than the primary universe. Since they are both, ultimately, illusions. It's an essential element of his story-telling.
He's used the same concept in a variety of his works including Silver surfer, Man thing, Spider-man, Dr Strange, Spectre, Dr Fate, Forever people, Supergirl, JLA, and that GL comic.
Like i said. This Hinduism theme is used quite frequently by him in many of his works, it can be found in all the titles that i mentioned above.
This isn't me trying hard as i can to invalidate a feat (i dont really care, frankly), im legitimately highlighting Dematteis' intention when he wrote the comic. I mean, you can go on believing that he intended a rookie Hal to create a fully fledged universe with ease, if you want, but considering the above info which i provided, i think everybody will think twice before acknowledging the feat.