mk47at: That's a good question. I would say yes, if you like the game.
Ashes adds to the main campaign.
Embers adds a new campaign and new races.
The Embers campaign is shorter than the main campaign so it is definitely a lot easier to reach the ending.
Have you played the free version?
There's more to it than this.
Ashes adds in one of the best melee classes in the game and another one of the more fun classes of the game, some pretty good lore, some items, and a random demon statue that you can interact with. It's small but worth it because the demons are actually interesting.
Embers is actually very large when you unlock everything. I say this because getting tinkers (the main attraction of this addon outside of playing as an Orc, it's a light crafting ability) on the main campaign is a very big deal, and there isn't a single class that can't benefit. For some it completely changes builds. The campaign though is definitely built for experienced players, in that it spoils about everything from the past one in some way.
Upcomming is an addon focused on Horrors, which is going to be like Ashes in that it adds to the original campaign but much bigger.