When exploring the Nether, I found that almost none of the biomes were generating properly except for the Nether Wastes and Basalt Deltas. When exploring the soulsand valley, the fog changes into its proper color, the correct mobs will spawn, but the biome is covered with netherrack and the nether ores instead of soulsand and soulsoil. The only thing that does generate are the basalt pillars. This also occurred in the Crimson forest, the only thing from that biome I could find were some weeping vines, but there were no trees anywhere to be found.