Grim's art style is actually really interesting!/gen It stands out in multiple ways, but mostly in the character designs.
Made at a time when 3D models in games were still very blocky, Grim managed to use this limitation to its advantage. The character designs are heavily inspired by Mexican folk art.
The skeleton characters were modeled after calacas, colorfully exaggerated figures of skeletons made from wood, clay, or, as far as I can tell, whatever other material you can think of. Calacas tend to be highly stylized, with more exaggerated shapes and proportions than real skeletons. They notably translate very well to animation such as in Book of Life, Coco, and Monster High, and Grim Fandango is no exception. Their simpler, more distinctive shapes can actually be captured really well with Grim's blockier, less refined models.
Mariachis in Grim Fandango.
Real mariachi calaca figures.
The same goes for a lot of the monsters, which seemed to be inspired by alebrije figures. (If you've never heard of alebrijes, check out this article! They're super cool!/gen)
Monsters from the Sea of Lament in Grim Fandango.
Image from the alebrijes Wikipedia page.
One of the cats from the Cat Tracks in Rubacava.
An alebrije from this article.
Alebrijes rely on striking and dramatic shapes and vibrant colors, meaning that, like the calacas, they mesh surprisingly well with early 3D graphics.
Now, according to the developer commentary in the remastered version of the game, the demons and some of the vehicles, Glottis and the Bone Wagon in particular, were inspired by the work of the cartoonist Ed Roth. (His Wikipedia page here if you're interested!) I wasn't familiar with Ed Roth prior to playing Grim, but after looking up his work, yeah, I see the influence!
Glottis and the Bone Wagon.
Grim's models and textures aren't nearly as detailed, but the spirit is there!
All-in-all, just like with everything else, Grim Fandango's art style bursting with charm and personality that more than make up for its outdated graphics!
Link to the complete review!