Summary:
Everything that is good about the Soul Harvest is what it took from the base game. The new things it brought were mostly making it worse (or stupid), which is pretty bad for an expansion.

To elaborate:
This expansion kind of broke it for me. The base game, I would recommend, even though that it breaks the lore in numerous places, but its inaccuracies pale in comparison to s**tstorm of randomness end bull**** the Soul Harvest presents.
Lore aside, the game got more boring overall. Weapons and armour that needed to be crafted in the base game and would be obtainable only if you did specific things (like killing a dragon) now just drop from enemies or in rewards. Why? It's boring as hell.
To be fair, playing as dwarfs was fun, but playing as dark elves, not so much.
The Vinculum thing was redundant and pointless. I think the developers were trying to do what BioShock Infinite did, but failed; it is barely important for anything in the game gameplay-wise and doesn’t really fit into the SF universe at all. It feels forced.