Their development philosophy, as stated in the v1.1.0 readme, is "Slow, steady, and infinite. I don't want you to finish the game. I want you to live in it." This explains the "Unlimited" branding—the game is designed to be a forever-WIP, with version 1.1.0 being just a step toward a theoretical 2.0 release.
Unlimited Pleasure uses or a similar 3D rendering engine, which is standard for many indie sandbox games. Waifston’s strength lies in lighting and expression. Version 1.1.0 seems to improve shadow rendering in the evening scenes, giving the mansion a cozier, more immersive atmosphere. Unlimited Pleasure -v1.1.0- By Waifston