Companion Donna Noble absorbed some of the Doctor's mind in the finale
The finale of the latest Doctor Who series has been greeted with a mixed response by the show's fans.
Speculation that he would regenerate after being wounded by a Dalek last week proved to be unfounded.
A number of fans wrote on the Digital Spy site's Doctor Who message board that this made it "an anti-climax".
Another fan hailed it as "one of the best things I have ever seen". The episode was seen by an average audience of 9.4 million people on BBC One.
The fact that the Doctor did not regenerate leaves the way clear for actor David Tennant's return.
A fifth series of the show is scheduled for 2010.
One fan wrote on Digital Spy that the episode was "a total let down for me".
"It felt rushed, sloppy and lacked something vital."
The fan added: "Too rushed, reached no conclusion, and well... after a string of fantastic, brilliant episodes, that was average."
But another wrote: "Tonight I had the same sense of excitement that I had when Tom Baker regenerated into Peter Davison.
"And I never thought I'd be saying that 27 years later."
And on the forums of the Ain't It Cool News website, a fan praised "a wonderful finale filled with touching, heartbreaking and downright brilliant moments".
They added: "We can all rest safe in the knowledge Mr Tennant isn't leaving (yet!)"
But, also on Ain't It Cool, another fan described the episode as "ultimately unfulfilling".
"Fair play to [chief writer] Russell T Davies, he's tried but he hasn't quite made it, going for style and bravado over substance.
"My Doctor Who is about storytelling."
In Saturday's episode, the Doctor was helped by a number of companions to defeat the Daleks and their evil creator Davros to save the universe.
Twists included the cloning of the Doctor.
The episode was written by chief writer Russell T Davies
Current companion Donna Noble, played by Catherine Tate, also absorbed some of his mind to become half-Time Lord.
At the end of the episode, the Doctor left his cloned self - who was half-human and as such will age and die - to live with former companion Rose Tyler, played by Billie Piper, in another reality.
The Doctor also separated from Donna, who had to have her mind wiped of all memories of their time together, before departing on his own in the Tardis.
Tennant will star in the lead role for a number of BBC One specials next year.
A fifth series, which will see writer Steven Moffat take over from current executive producer Russell T Davies, is due in 2010.