If Pillars of Eternity was cribbing the style of Baldur's Gate, Tyranny is more in line with Planescape: Torment, not to say that Tyranny reaches that lofty height but in that it deals more with talking to people and working things out through dialogue more so than other Infinity engine-style RPGs. It also deals heavily in reputation, both with factions and with individuals, that Obsidian previously used in New Vegas. One of the only major issues I had with Pillars was that it felt a bit bland: the world, the locations, and even the story just felt like Obsidian was still working within the confines of D&D. Tyranny, however, really feels like Obsidian wiped the slate completely clear and built this world from scratch. It's got more diverse and interesting locations, really good and bizarre characters, and a backstory that feels fresh. I like how you start as basically just a bureaucrat sent to stop two factions of the overlord's army from squabbling with each other.
Combat's great, by the way, feels like a step up from Pillars. Less abilities overall, but they're more meaningful. They've also added in special abilities that require a party member and the main character to cooperate for more devastating effect than ordinary abilities. It's also got less combat than Pillars, so it hardly ever feels like you're just grinding away against trash mobs.
I've played for 17 hours so far, still seem to be quite a ways from the end.