In Hexen II, we saw architecture reflective of the Egyptians, Meso-Americans, and other recognizable styles. In Heretic II, they've created their own. As Corvus progresses on his quest, he is taken to his home town, an amphibian city, insect-like hive, and more. Each land not only has it's own architectural rules, but also blends the fantasy elements of the game into the level design. Again, a brilliant end result from Raven.
Enemies are varied and interesting, and generally native to a certain region.
Bosses are very imaginative, and don't necessarily come at the END of the hub. A health bar appears when a boss is on-screen, so you can see what kind of damage you're doing to it. Weapons are absolutely non-standard, which is a refreshing difference in the 3D action game genre. You begin with your staff, simply a stick at the beginning of the game, used for striking and pole-vaulting. This is powered up as the game progresses, so your standard weapon actually keeps its value.