Play Unity today on a top-tier PC and you'll be pleasantly surprised at just how beautiful it looks.
Ubisoft scaled up virtually every element of the last-gen engine, with enormous increases to environment detail (including building interiors), an NPC count pushed into the hundreds and a cutting-edge rendering engine with sensational, physically-based lighting.
In retrospect, perhaps Assassin's Creed Unity was simply too ambitious from a technological perspective.