This article at Gameplayer uses their hands-on experience with GTA IV and Euphoria engine to propose that the company NaturalMotion will become the best buy on the market folling the release of Rockstar's game. NaturalMotion manke the Euphoria Engine.
"We've played the game extensively and Euphoria's power is undeniable. In the mother of all open-world games, it utilises the mother of all open-animation technologies in a city so detailed and enormous the domino effect described above is, for all intents and purposes, endless. It's literally a case of 'if a butterfly flaps its wings in Alderney…'"