Written by Gareth Roberts (The Shakespeare Code, The Unicorn and the Wasp and Planet of the Dead) this was an interesting change of pace for an episode. Pretty much as close to a comedy as Doctor Who will ever get with genuinely funny lines and situations showing us that Doctor Who could have been a family sitcom with this premise.
The downside is that I found it a bit difficult at times to swallow that the Doctor was quite so unfamiliar with Earth customs as he was portrayed in this episode. I know sometimes he acts quite alien and odd and there are nuances of human behavior he doesn't get but by his Eleventh incarnation I think he's be familiar enough with humans in the 21st century to know they don't greet each other with air kisses and that Englishmen have an insane love of football. So while his disinterest with money and its value is very consistent with every previous Doctor, some of the other acts seemed at odds with his previous incarnations knowledge of humanity. It was nice to see his love of cats restored though after the Tenth Doctor said he hated them in Fear Her.
As a result of these two things, I find myself conflicted with the episode on one hand enjoying the comedy and situations and on the other hand the fanboy inside me is saying, "But he wouldn't really act like that would he?"
I really liked the headbutting telepathic contact scene. That was a really interesting way for the Doctor to pass on his life story and yet it also showed why he doesn't do it very often despite it being a potentially very useful ability. This was the fourth time we've seen a picture of the 1st Doctor and the third time for the 2nd Doctor this series which is a welcome surprise.
I'm not sure what to make of the psuedo-TARDIS. Especially since we are not told who or what built it. Its always implied that the TARDIS is immensely difficult to build as no other race outside of the Time Lords has ever mastered it so it must be a terribly advanced race to even attempt getting a partially working one. Even the War Chief was unable to replicate them completely as he was only able to construct sub-par SIDRATs for the War Lords. I'm not sure they will ever follow up on this mystery but I would sure like them to.
Overall a success I would say especially as a comedy but not one of my favorites of the series so far.
Here's my list of favorite ninth stories for every Doctor:
1) Mindwarp by Philip Martin
2) The Daemons by Guy Leopold (Pseudonym for Barry Letts and Robert Sloman)
3) The Abominable Snowmen by Mervyn Haisman and Henry Lincoln
4) Battlefield by Ben Aaronovitch
5) Planet of Giants by Louis Marks
6) Boom Town by Russell T. Davies
7) The Android Invasion by Terry Nation
8) Love & Monsters by Russell T. Davies
9) The Lodger by Gareth Roberts
10) Snakedance by Christopher Bailey