The clear description for Shadow was powerless. He felt powerless, vulnerable, lacking the energy he knew built up inside of him. It's like that human form took away what made him the Ultimate Lifeform, and that was... bad.

He wasn't about to admit that to Sonic, of all people, so he improvised with a soft snort that, coming from him, seemed somewhat dignified.

"Irritating. The human body would take getting used to. I have no need for that."