Yes, Kirk WAS obnoxious; I think the point in the film was supposed to be that he was young there and grew out of the extreme attitude, just as Spock grew to control his emotions better as time went by.
However, I never really liked the original series and only became a Trekkie with The Next Generation and subsequent Trek series.
They all speak English thanks to that wonderful gadget, the Universal Translator, which ranks right up there with the transporter and the warp engine as innovations that haven't been invented yet. I can't wait!