I'd heard of this movie before and had to check it out - the scene I watched where he was speaking to who I assume is the female lead sounded like an American and an Italian both speaking perfectly passable Esperanto. If I were to nitpick his i's were a little soft - Esperanto i's are canonically pronounced ee - but Esperanto was made to accommodate lots of different accents without losing comprehensibility and it did that here. I actually found his Esperanto easier to follow than the girl's, but that's probably because I learned Esperanto from people speaking it with Canadian accents.

Shatner speaks Esperanto with a perfect native accent. Everyone else is pronouncing it wrong.

When I watched Incubus I remember him sounding very much like he was trying to speak Italian. My only basis for comparison are some podcasts in Esperanto I've listened to, and completion of the duolingo course (I've forgotten everything).