As the official Anti-pope of the OSR, I feel that it is my (anti)papal duty to introduce you to various heresies for your own edification and corruption. This is the first of them.
4th edition D&D is the perfect system for Glorantha.
Glorantha is an old-school setting in which almost everyone uses a little magic to make their lives easier. 4th edition D&D is a setting reviled by old-school grognards because all characters have "powers" and supposedly these powers "make everyone a wizard." All that shit grogs don't like is actually magic in Glorantha. The fighter uses a power that moves all his enemies closer to his sword sweep? Yeah, he learned that power from the cult he belongs to. The ranger's weapons are suffused with crackling lightning? He worships Storm Bull. What now, grog?
Hell, Glorantha has three distinct sources of magic: sorcery (the result of arcane study), divine magic (gained through initiation into cults), and spirit magic (gained through dealing with spirits). 4e D&D has power sources that map neatly to that tripartite division: arcane power (sorcerous magic), divine power (the power of the gods), and primal power (the power of natural spirits).
Glorantha is also a game where the characters can re-enact the quests of great heroes and gods to gain a portion of their mythic abilities. 4e D&D is a system that allows for Epic Destinies modeled after mythic archetypes.
Glorantha has elves that are plant-people. 4e D&D has these guys:
Glorantha as a playable race of Dragonewts. 4e D&D has these guys: