He returned home much inspired, no wonder the plan had worked.

Inspired : fill (someone) with the urge or ability to do or feel something, especially to do something creative.
Overwhelmed : have a strong emotional effect on.
Dispirited : cause (someone) to lose enthusiasm or hope.
Disillusioned : disappointed in someone or something that one discovers to be less good than one had believed.
Sceptical : not easily convinced; having doubts or reservations.

Antonym of Inspired is Dispirited