Silence and the Fury finally makes Beastmen interesting and adaptive without having to constantly re-crush enemies you don't want to thanks to the totems, and the gameplay for lizardmen becomes a lot more driven with the required missions for the new Legendary Lord.
Downside: Beastmen become ridiculously good. They'd be OK against human opponents, but AI has no idea what to do about the totems, and they're easy to keep out of your bloodgrounds, making the campaign a bit too easy.
The new Skinks finally add a cheaper set of decent units for the Lizardmen, giving some options for the early game or for raiding parties compared to the old forced-turtling they had. However, the flaw is that only a couple of the Lizardmen Legendary Lords can use them well
The campaign quests for the Vortex aren't otherwise massively interesting compared to other DLC, but they're solid enough campaigns.