AtomicPope
Hero
4e World Axis is best suited for RPGs, especially DnD where there are decades of campaign settings to draw on. The World Axis was the easiest, by far, for new players to understand. I was teaching all of the children (friends and neighbors included) DnD during the 4e era and even the youngest, who was 8, caught on. The World Axis captured all of the thematic fantasy of DnD Cosmology without being bogged down in strange rules/rulings. It managed to merge Planescape and Spelljammer without ruining either. It's definitely on of the things 4e got right.