Their best marketing tool would've been a good old demo, if you ask me. The first portion (character creation, conquest mode and the first area) does a great job in how it shows the player what the game is about. Unlike PoE, it introduces the setting, lore, reactivity and combat gameplay really well. My guess would be that not everyone who likes the first couple of hours will necessarily like the game, but if you don't like the first couple of hours, the game is probably not for you.
For those who didn't watch any character creation video (I didn't know this before playing), conquest mode is basically a series of decisions that determine the key events in the invasion of the country where the game takes place.
You can see it between ~11-28min here:
It does have a major flaw, however. There's one event where you have to choose between 3 options that are tied to a combat skill. I don't know if you can learn them later on, but they sound pretty powerful, and the one I picked is very useful. The main problem is that they're related to specific playstyles, and I think players are more likely to care about the skill than the decision, so they'll just pick the best skill instead of choosing the option they truly wanted.
I tested different decisions and also compared mine to my friend's, and the reactivity is definitely there. It changes how the 3 major factions treat you, how people address you, and your standing with both factions. My friend also said there are bigger consequences down the road, but I don't know yet.
It's an optional tool, by the way, though I don't know what happens if you choose "quick start" and skip it. Probably a neutral start, I'd guess.
I think the problem may be less the "marketing" as such and more the "branding", without which marketing has less impact. Again, they haven't tied the game closely enough to Pillars of Eternity. They should have ridden on its coattails all the way.
I didn't read much about it before playing, and I was surprised by how similar the combat and systems are. Combat plays pretty much the same, and anyone who played PoE will know almost all hotkeys and controls without reading anything.