Wallers will be hard, especially for ranged classes, but elites with 'avenger' affix look much more dangerous. If you kill one mob from the pack, others get dmg increase (stacks up to 3). In theory, best way to deal with such pack is to get every mob to 10% hp and then kill them all at once. Theory is one thing, aoe effects from your own skills is another. Hardcore is looking very hardcore atm. I hope they won't nerf the game after it's released.