Really enjoyed Glenn's great overview of Robert E. Howard's only Conan novel. I pretty much agree with the good and bad points raised. The discussion of the Grail/Fisher King/Wasteland inspirations was really interesting - not something I'd ever considered from Howard's work before.
On the subject of Howard's hasty writing of the story, not only is the first part a re-write of The Scarlet Citadel, but once you've read a lot of the Conan stories, you notice that most of the material in the second part is, if not actually re-written, then very derivative of stuff from elsewhere. That's not really a criticism as such, but I'd say Hour of the Dragon is a bit harder to enjoy as a veteran Conan reader than as a relative newcomer. Actually, the more I think about it, the more I think this would be a really good introduction to Conan for someone who has never read any of the stories before. It's a lot longer than the average, but it has pretty much everything in it, so you can read it an get an idea of whether Conan is for you or not.
In terms of sub-genre, can we say it's "epic sword and sorcery"? Is that a thing? I feel like based on your criteria, it would fit more into epic fantasy than strict sword and sorcery. But at the same time, the focus remains (largely) on Conan and the threat(s) to him from the antagonists (especially Xaltotun), rather than on the world-ending, epic threat. Admittedly, this is mainly thanks to the more narrowly focussed second part, which as you said, is more traditional sword and sorcery.
Actually, I feel like one weakness you didn't cover is that Howard too often relies on an omniscient narrator to explain what's happening outside Conan's POV, especially in the transition from part two to part three (probably another result of his writing in a hurry). Personally, that dragged it more out of the genre of sword and sorcery than the epic threat of Xaltotun. In fact, I'd go so far as to say that Xaltotun isn't unusual for a sword and sorcery antagonist. What's unusual is that he makes progress with his plan before being stopped, whereas in a more traditional sword and sorcery tale, the protagonist would have stopped Xaltotun (or whoever) not long after the resurrection, maybe even after witnessing it. This probably comes from the story being a novel rather than a short story or novella, so the stakes need to be higher to keep things going. And my experience with sword and sorcery is limited to mainly Howard and a few short stories by other authors, so I don't have a particularly wide perspective and could be wrong.