Because it doesn't plug hundreds of high quality textures and such into the game, it seems to run fairly smoothly, while also leaving itself open for a potential future HD remaster. (quillstreak.com)
Additionally, it looks like it may even be possible to introduce higher quality textures in the game. (wccftech.com)
The environments are also more detailed, especially in the texture department: surfaces are much sharper and more defined as a result of higher quality textures. (eurogamer.net)