The Captains pinpoints a specific time in Shatner's life, chronicling his early days as an actor until his star-making role as Captain Kirk, replacing Jeffrey Hunter's Captain Pike right when Gene Roddenberry was trying to get Star Trek off the ground. Shatner is also executive producer on the project, which will air in 2011 on Canada's Movie Central Channel according to Trek Movie.
The older Shatner gets, the more willing he is to be self-deprecating, but he's still pretty bull-headed when it comes to Trek. Check out his amusing interactions with Leonard Nimoy in "The Captain's Summit" special feature on the Star Trek Original Motion Picture Collection blu-ray (where he stubbornly pretends he's never seen a single episode of The Next Generation), or his roundabout way of using the press to communicate with director J.J. Abrams during the making of 2009's Star Trek.
My hope is that The Captains will reveal more about Shatner than he intends to reveal; that by placing himself in the director's chair, his construction of the film will say more about himself than any talking head interview or archival footage. We'll find out soon enough.