They're designed and animated VERY well. Just the kind of grotesque beasty you expect hanging out in an old dungeon.
Simon's reaction to the Mushrooms pretty much sums it up: http://www.youtube.com/watch?v=cz7NEax41LI - (Warning: a bit of swearing. )
(Him SCREAMING his face off when they get pounced on by a spider in the last of their episodes is brill too. XD)
I was telling a friend of mine about this game, and how it was based off of those old dungeon crawlers and was an indie game. When he actually saw LoG he seemed really impressed with the graphics and the monster designs and animation. He clearly wasn't expecting this level of quality.
I showed him the Goromorgs in particular, and he thought they were pretty damn cool. It helps that we've been playing a lot of Arkham Horror recently. They're like some twisted lovecraftian stuff.