I liked balance within the Nighthaunt tome the most when it was released, at least from the armies i played. It fell off a bit in the end though. Flavourful abilities and special rules and pretty balanced powerlevel units.
If 4th edition doesnt do it ill just stick to playing 3rd edition for a while. There is a lot there for me to keep playing/exploring. It could be better, but imho 3rd was pretty good as far as editions go for GW games.