What does the RuneQuest system do that's amazing?
I think it's the world of Glorantha rather than the system. Greg Stafford is just brilliant creatively, imo. His concepts are that bit more imaginative and weirder than those of the creators of other secondary worlds. He studied mythology and folkore extensively and he really knows his stuff. I think he has a good ear for names too.
Why? What is it about those particular gods that strikes your fancy?
The Red Goddess is unlike most of the other gods, she appeared in history, the others all came into existence before there was such a thing as time. (See what I mean by weird?) She's the goddess of the Red Moon, which was created by ripping a huge mass of material out of the ground and setting it floating in the air. Because of this she's in conflict with Orlanth, the storm god, as he sees this as trespassing in his domain. The Red Goddess embraces Chaos, which is regarded as evil and alien by most Gloranthan cultures.
The Lunar Empire, which follows the Red Goddess is pragmatic, meritocratic, promotes equal rights for men and women and is hated by almost everyone partly because of its ties to Chaos.
Nysalor/Gbaji was created by a group of mortals to be the perfect being. His religion is Glorantha's equivalent of Buddhism but he is also Chaotic and seen as evil by many.
Thanatar is, I think, a combination of two earlier gods, the head of one on the body of another. His followers gain power by garrotting and beheading their victims, whose knowledge and skills they can then use by keeping the severed head.
I'm not doing those ideas justice and probably misremembering them quite badly, but you can see how bizarre and complex these gods are.
Storm Bull and the Crimson Bat are a lot simpler. The first hates chaos. His followers guard a great magical stone called the Block because the Devil is imprisoned beneath it. The stone is very valuable so that's something for PCs to do right there.
The Crimson Bat is a manifested god. It's a gigantic red bat covered in blood-spraying eyes that flies around the borders of the Lunar Empire eating people, who are procured by the worshippers and priests that travel alongside.
Mostly what I like about these gods is the richness and weirdness of the concepts. With Storm Bull I just like the adventure idea of the Block.