Unfricking believable. Actually, its very believable, that's why its so great so far. Played about an hour through most of the canal stuff.
SMALL TINY SPOILER
There is one part where you turn the corner and watch a barnacle eat a crow. It looked great! But the true genius was when I quick-loaded and replayed the scene, killing the barnacle before it ate the crow. That was a wow moment for me!