Thats because he use lighting (2 point or 3 point) on his characters
And my guess is that he is using photometric lights (spot lights) instead of mesh lights here.
90% of the other games here dont know how to setup proper lighting or use any lighting at all.
this is what creates the 3d depth in this game.
other games looks flat and dull because of lack of lighting.
with proper lighting and the characters comes to life.
exactly like you see here.
Great work to the developer!
Example of 2 point photometric lights
(Sophia a wife and a mother)