Journey's End is the finale of Series 4. Its one of the worst episodes of the Russell T. Davies Era.
TLDR: This episode is shit.
The surprise cliffhanger last episode was a shocker. However as the days went by in the week long wait for Journeys End the bullshit was starting to smell pretty bad when you actually thought about it and realized how impossible it would have been for them to keep a new doctor a secret. We also knew that Moffat would be taking over and his name was nowhere to be found on these episodes. So it was basically just waiting to see what cop-out bullshit Davies would pull this time..
So The Doctor begins to regenerate but before he changes his body he expels all the regeneration energy into the hand so he doesn't have to change or some bullshit. It was pretty retarded. Typical. But its not like it could get any worse or anything....
Then Sarah Jane in a completely out of character moment cowers in fear of the Daleks but is saved by Mickey and Jackie appearing with the reality jump thing. (How did they know she was screaming and about to die? Who knows. RTD doesn't, that's for sure)
Daleks then locate the Tardis and take it to the Crucible. Everyone walks out except for Donna because shes stupid and then the Daleks drop the Tardis in flames and everyone thinks it died along with Donna. But actually Donna crawled over to the Hand touched it causing a clone doctor to appear. But hey, its not like it could any worse right....
The Daleks call the The TARDIS a weapon in this scene when they try to burn it. But it makes absolutely no sense. The Tardis has no offensive capabilities at all; it's technology, but it isn't a "weapon".
Then a bunch of pointless shit happens and eventually all the companions are standing around in front of Davros with The Doctor in "holding cells" Davros spouts off some handfisted dialogue about the doctor turning companions into weapons while Tennant does his usual gurning and over the top acting.
Davros says the doctor "fashions ordinary people into weapons" during this scene which is just plain wrong. They have free will, so they aren't weapons. Weapons are tools; guns don't choose who to shoot. At best they're soldiers, and even that's a stretch. Its not even a moral debate. Its just wrong.
Anyways Davros is completely wasted as he gets barely any lines, barely any screentime and the little screentime and lines he does get are absolutely retarded.
Meanwhile Clone 10 and Donna are building a weapon to try and come save the day.
And then he says hes going to use the reality bomb to blow up the entire universe. (Wow. this surely over the top machine wont get resolved in some evenly just as over the top resolution....)
Then the Tardis appears and Clone 10 and Donna walk out. Davros zaps Clone 10 and he drops the weapons and then gets trapped in a holding cell then Davros blows up the weapon. (Oh no, its over, the universe is over, whatever will they do, they cant save the day now) Davros starts the countdown for the reality bomb. Then Donna presses a bunch of buttons on the handy Dues Ex Machina machine and spouts off tons and tons of technobubble. (bio-electric dampening field with a retrograde field arc inversion for one example)
We then learn that the regeneration made her part time lord so shes super duper special and smart now. Then Clone 10 spams buttons on the Deus Ex Machina machine and destroys all the Daleks causing real 10 to yell at him for some reason. Real 10 is a fucking cunt. Then explosions begin and everyone runs into the Tardis and 10 tries to save Davros for some stupid reason. Real 10 is a fucking idiot. Davros tells him to fuck off however.
Afterwards they all get into the Tardis and 10 teaches everyone what buttons and levers to use and they all tow the planets back to their rightful places while cheery music plays and Freema Agyeman breaks the 4th Wall in one of the worst scenes of NuWho.
Everyone then gets dropped off. Mickey and Martha head off together because they're both black and RTD is a racist. Rose gets dropped off back at the beach and gets Clone 10 as her own personal fuck toy. They kiss each other while real 10 looks on sad thats its not him who will be fucked by Rose. Real 10 and Donna leave.
Finally we find out that The Time Lord stuff is too much for Donnas brain, shes going to die. The only way to save her is to remove all memory of the Doctor and travels from her brain. Catherine and Tennant are both equally terrible in this scene with tons of melodramatic overacting. 10 drops her off and tells Wilf and Sylvia she can never remember him and then he leaves and the episode ends with more melodramatic acting from Tennant.
In the first Doctor Who Confidential that shows Russell T. Davies' office, you can see a well-thumbed copy of the VNA Sky Pirates, taken out of the complete collection on the shelf. Coincidentally, that book has a plot device called the reality bomb. Totally just a coincidence. We all know that RTD never read any of the novels, despite having a complete collection on his shelf, and having written one of them. Anyway, Sky Pirates would have made a much better TV episode, but since its reality bomb doesn't threatens to blow up the whole universe plus all the other places and even more than that too, it could never be an RTD finale.