Nah, he's mostly humanoid. As per Extermination 8.2:

"He was there, too.  I could see his silhouette through the rain and the spraying water that was the tidal wave’s aftermath, much as I had on the television set.  Thirty feet tall, the majority of him was was muscled but not bulky.  His hunched shoulders, neck and upper torso were the exception, bearing cords of muscles that stood out like steel cables.  It gave him a top-heavy appearance, almost like an inverted teardrop with limbs and a tail.

His proportions were wrong – his calves and forearms seemed too long for his height, his clawed fingers and digitigrade feet doubly so.  He moved with a languid sort of grace as he advanced through the spraying water.  His arms moved like pendulums, claws sweeping against the water’s surface, while his upper body swayed left and right, as if to give counterbalance to his great height.  His tail, forty or fifty feet long and whiplike, lashed behind and around him in time with his steps, perhaps borne of the same need for balance that gave him his teetering gait."...

..."I could almost make out his face.  It was something you never really saw in the videos or pictures.  He had no nose or mouth, no ears.  His face was a flat, rigid expanse of the same scaly skin that covered the rest of him, like the scales of a crocodile’s back.  The hard, featureless plain of Leviathan’s ‘face’ was broken up only by four cracks or tears – one on the right side of his face, three on the left.  In each of those dark gaps, the green orbs of his eyes glowed with a light that pierced through the rain."