In 1989 the BBC canceled the old Doctor Who show. In 1996, Fox TV broadcast a two-hour one-shot, intended as a pilot for a revival, starring Paul McGann as the Ninth Doctor. Alas, it didn't take and it wasn't until 2005 that the show was successfully revived.
In the meantime, Paul McGann was the official current Doctor: in magazines, comics, spin-off novels and audio releases from Big Finish Productions, Paul McGann was the Doctor. Fans, of course, argued the point, but that's what fans do. However, the current BBC has clearly accepted McGann's appearance as canonical in various ways, starting with 2007's "Human Nature".
It's great to see Paul McGann appear in this prologue to next Saturday's Fiftieth Anniversary Special. It's fun for me, as a fan of the new and classic shows, to see McGann finally get a chance to officially reprise the role and to mention some of the companions that accompanied him in those years of exile. It feels like vindication.
However, there is so much crammed into its six minutes -- McGann, Karn, the Last Great Time War, the companions and more -- that I had to watch it twice to catch all the references. To a fan of the modern show, unfamiliar with McGann, it will be utterly incomprehensible.
Still, as an act of personal sentiment, I'm glad it was done. It's also a nice teaser; did McGann film this as part of a super-secret appearance in the 50th Anniversary Show? I'll have to wait a week to find out.