A line of posters for the forthcoming film Star Trek, on the first day of ShoWest, the largest annual convention for the motion picture industry on March 30 in Las Vegas. ((Chris Pizzello/Associated Press))

Sci-fi fans in Texas were stunned — and then elated — this week when actor Leonard Nimoy appeared onstage and swapped their expected screening of 1982's Star Trek: The Wrath of Khan for the new Star Trek film.

The Trek icon popped into Austin's Alamo Draft House on Monday night and surprised the audience with one of the first public showings of the upcoming prequel film by J.J. Abrams.

Many audience members later shared overwhelmingly positive reviews of the new film online, with one viewer calling it "the best Star Trek movie ever. Yes, it even beat Wrath of Khan."

The movie had its official world premiere at Australia's Sydney Opera House Tuesday night.

Abrams's Star Trek is a reimagining of the late Gene Roddenberry's enduring series.

The film chronicles the early days of the original characters, most importantly human commander James T. Kirk and Spock, his friend and colleague hailing from the planet Vulcan, as they train at Starfleet Academy.

It is set for North American release on May 8.