Digital Foundry : Tech Analysis: The Witcher 2 EE
Full analysis here
In summary then, it's clear that The Witcher 2 has the performance to match the spectacle.This may well be a PC conversion, but the level of technical accomplishment we see here is more in line with what we'd expect from a top-tier first-party studio designing a game directly for the strengths of the host console hardware.
Compare and contrast with a comparable technology - such as Anvil, the Assassin's Creed engine, which has gradually evolved across four games thus far. On its first attempt, CD Projekt RED has bested it in virtually every way, from characters to environment detail to lighting to effects work - and it runs more smoothly to boot
Full analysis here