Episodes Three and Four- Aliens of London and World War Three- are not individual stories at all but one split into two. The outstanding feature of these episodes is the really sad schoolboy humour. Here's a hint for the writers: farting isn't funny past the age of about seven- get a life.
The story begins with Rose and the Doctor back in present day London and we get to see the effects on Rose's family and friends of her travelling with the Doctor- though they've only been away a few days a year has passed on Earth- once again the TARDIS proves to be not quite accurate enough. This family drama segment is played quite well and it doesn't distract from the main plotline- involving an alien ship crashing through Big Ben and into the Thames River. London is in a panic and we get a few scenes of news reporters following the story- as the Doctor and Rose are forced to watch on TV. It soon becomes apparent that not all is as it seems- as a body is pulled from the craft we learn that the Prime Minister and cabinet cannot be reached or found- an obscure MP finds himself catapulted to power in No. 10 and it's here that much of the action takes place.
I don't want to spoil much more of the story but too much of this episode remains rooted in pathetic schoolboy humour- again the sense is that this was an episode aimed at kid's TV, not prime time viewing on a Saturday evening. There's simply too much juvenile material in this to really enjoy it- and once more the scenes which don't involve talking heads aren't directed too well either. For a double header episode it sure isn't done very well at all- in fact, given the material and the childish way it was handled, this would have been better served as a single episode. Now, if it had been executed properly- and the direction and the writing would have needed an awful lot of work- this could have been a fantastic three or four parter. The core concept- alien infiltration at the highest levels of power- is superb, and it could have made for a suspensful, intriguing and exciting episode. This two parter just falls flat though. The final section could have been claustrophobic and scary, like something out of Aliens, but the creators of the show don't seem to understand horror or science fiction elements at all.
One other complaint- and this is not just limited to Doctor Who but most shows/films made now- is that when a special effect needs to be done, film-makers too often turn to CGI first- there are a few instances in this show when traditional effects would have been more believeable and would have given a greater sense of danger- if CGI isn't a 100% convincing then we know the actor is running away from nothing- and what's scary about that? Very disappointing indeed. Oh, I almost forgot- without giving away the actual plot, when you do discover what the aliens are up to, and remember these are aliens with interstellar craft at their disposal, you have to think- well, why did they need to do all that, couldn't they just have done it themselves? It makes the whole two episodes seem completely pointless. The writers on this show really have to improve, and start thinking about what they're scribbling.