If you're looking to recreate the Pillars of Eternity look and feel, I would go with the engine that started it all: the Infinity engine. I'm not sure the Infinity engine (or its successor, the Aurora engine) are publicly available. However, here's an open source implementation of them:
http://www.gemrb.org/wiki/doku.php?id=startWith that in mind, I think you should first consider what you want to do, and than choose the engine. If it's a 3d game, you're better off with a 3d engine like Unity, Unreal or Lumberyard. If it's a 2d game - you might want to focus on a 2d engine.
As with everything else - proper planning at the start, will save you a lot of headache later.