Inferno has seen almost all of its units improved, which isn't necessarily a sign of good balance.
Necropolis, however, is still quite well-balanced. The enhanced vampires lack a retaliatory attack;
the resurrecting liches don't have a cloud ability;
the new ghosts have a questionable ability, while the old one was very useful but rarely used because it was very specific.
The new Nazgûl are also good. Their ability deals such a negligible amount of damage that it's clearly not better, but because it affects everyone, it's not worse than Deadly Touch.
Dragons – I'm not sure about them, but the old curse is better than the debuffs to spirit/luck;
Skeletons – here, the balance isn't quite right. The new ones are simply excellent at targeting ranged units, stunning, and are quite durable, cheap, and numerous, making them much more useful. The old ones shot, but without reaching hundreds of damage, they didn't represent a significant threat. Perhaps only with Battle Fury and/or an amulet that increases damage.
Zombies – I can't say anything about them; both the old and new ones are useless after vampires appear.