It's Trek done 2001: A Space Odyssey style. (I'd be surprised if Kubrick wasn't ever considered to direct, although he would have been busy prepping The Shining.) Having seen it opening weekend on a huge screen, that's where it worked best. It's probably not the movie to introduce newbies to Trek though.

Why would you be embarrassed by an overture? Lots of movies had them. The oath line probably should have been cut, since it's never explained in the theatrical version that Deltans have no sexual inhibitions compared to other species. Gene Roddenberry projecting his fantasies again. ;)

At the time, it was the first new live action Trek since 1969. Old cancelled tv shows just didn't come back from the dead in those days. Trek took a long twisted path back to life, almost becoming a new series, (Phase II) and then becoming a big budget film in the wake of Star Wars' success. In 1979, this was a big deal.