(This post mostly cribbed from a reply to
greylock )
Amazing dialogue.
Superb acting.
Great hints at future plot arcs.
But...
The Tardis-jury-rig from the Doctor was implausible -- the dead Tardises had been utterly drained of power, as had Sexy, so how were they able to get the jury-rigged one running? Likewise, putting Sexy back into a dead Tardis control room, with *both* of them having been drained of all energy -- nah.
Conceptual villain ("I suck all the life/power out of your space ships from Beyond Time And Space) was OK but we've seen much the same thing several times in Blake's 7 / Farscape / Marvel comics etc.
"Possessed" corridors/planet-surface used to toy with humans as playthings -- straight out of Ellison's _I Have No Mouth But I Must Scream_.
So not *hugely* original, and not totally lacking in plot holes. But still good, and still lots of fun.