The prologue of Star Trek was one of the most emotionally powerful sequences in a movie I've ever experienced and is arguably the best part of the movie. This is due in no small part to Hemsworth's performance. He did a great job and set up the title reveal perfectly.
I also enjoyed his acting in Thor and Avengers but I judge him differently there since the character has a much different personality. I do think Thor is too broody in Avengers but I don't blame Hemsworth for that. Hopefully he'll continue to be great in Thor 2.