#2 The Witcher 2: Assassins of Kings
Image Credit: Deadthrills
CD Projekt RED and its games have come a long way since the days of the Aurora Engine. The aforementioned Aurora Engine was first developed by Bioware to power Neverwinter Nights. It was heavily modified by the Polish developers for use in The Witcher.
The team went on to develop its own in-house engine, called RED Engine. It's good, and it puts most other engines to shame thanks to the fact that it was developed for the PC.