She’s not horrible-horrible, just a bit bland and bossy though nowhere near as bossy as Yen can be (but I love the whole chemistry Yen and Geralt have, so 
).
But she does do a very shady thing that the player could only know is a shady thing if he’s read the books… or played W3. In the books she’s kind of this adoptive daughter to Geralt and Yen/a sister to Ciri, even though she has a giant crush on him. But in W1 Geralt loses all his memories and she seizes the opportunity to pose as the love of his life and not telling him anything about Yen *or *Ciri. In W2 Geralt slowly starts remembering Yen, and in W3 he remembers everything and starts actively looking for her.
I’m not sure you can openly confront Triss about it in W3, but Yen is pretty pissed off about the whole thing as you may have seen. It *was *a good bed - it starred in the opening scene of the first game :).
[QUOTE=Simplicio]
I played through the vanilla game already. Does the DLC just add extra quests, or do I start a whole new area/storyline or what?
[/QUOTE]
Heart of Stone is an additional questline in the Novigrad area (plus it fleshes out the whole NE of the map with new stuff, a few more quests and contracts) with some pretty great bits. Blood & Wine is a full blown expansion set in another country, new map new monsters new characters new Gwent deck etc…