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troperville

Emperor Dalek: You cannot hurt me. I am immortal.
Bad Wolf: You are tiny. I can see the whole of time and space, every single atom of your existence. And I divide them.

When we left our heroes, they were staring down an absolutely ridiculous number of Daleks. Who turn out to be mutated humans, trapped in their pepperpot cans forever.

The Doctor and Jack rig a force field out of Margaret the Slitheen's surfboard, and go fetch Rose. Jack tenderly kisses Rose and the Doctor goodbye on their lips, and goes off the stall the Daleks, knowing that he probably won't survive. ^note The Doctor tricks Rose into going back into the TARDIS and sends her back to her own time to keep her safe. He activates a hologram recording that tells Rose to live a normal life, let the TARDIS die, and experience all she can as a regular human girl.

Rose won't have any of it and, looking for a way back, notices the words "Bad Wolf" everywhere around her in cloudy grey London. For the first time, she realizes that it may not be a warning at all... it may be an inspiration. She talks Mickey and Jackie into ripping apart the TARDIS to expose the ship's living telepathic core to her.

The Daleks approach the comms centre of the satellite as the Doctor is still preparing his wave attack, and they EX-TER-MI-NATE anyone they encounter — including Lynda and Jack. The Dalek Emperor tells the Doctor to make his choice. Will he be a killer like he was in the Time War, murdering every last human on Earth to destroy the Daleks? Or will he be a coward and let nature take its course? The Doctor realizes that he can't bear to repeat the actions he took during the Time War, and says that he'd be a coward, any day. Even if it means letting those mutated humans live on as Daleks forever. Even if it means he'll have to sacrifice himself.

Just as he's about to be murdered, Rose steps in, with time itself pulsing through her from the TARDIS core. As a catalyst for the Time Stream, she's become a literal Goddess from the machine, and she promptly kills every last Dalek she can find with a single word. On top of that, she scatters the words "Bad Wolf" — the name of the TV station — throughout time, space, and parallel dimensions, as a sign to herself. Oh, and she revives Jack. Remember the last time she saved someone who was supposed to be dead? What Could Possibly Go Wrong?

With all that, she collapses, and the Doctor, grinning, tells her... "I think you need a Doctor". He absorbs the full force of the Time Stream from her body by kissing her. It's a beautiful moment until it kills him.

Jack is left behind on the satellite so he can go star in Torchwood. The Doctor regenerates into David Tennant. Rose doesn't remember a thing, and is terrified when a strange man is suddenly bouncing around the TARDIS. From there, the ending segues into Doctor Who 2005 CiNS "Doctor Who: Children in Need".

Tropes

Arc Words: The meaning of "Bad Wolf" is finally explained. It doesn't have any inherent meaning, but was scattered across time and space by TARDIS!Rose to show normal Rose the way back to the Doctor.
Big Damn Kiss: Between Jack and Rose, Jack and the Doctor, and the Doctor and Rose.
Big "Shut Up!": "I think you're forgetting something. I'm the Doctor, and if there's one thing I can do it's talk. I've got five billion languages and you haven't got one way of stopping me, so if anybody's going to shut up, IT'S YOU!!"
Chekhov's Resurrection: Captain Jack's resurrection by an unbelievably powerful but inexperienced omnipotence will have a huge effect on his future story lines.
Continuity Nod: Turning dead humans into Daleks is another idea repurposed from the period after everyone stopped watching the first time.
Crowning Moment of Awesome: Rose transforms into a physical god, the Bad Wolf. "You are tiny. I can see the whole of time and space. Every single atom of your existence. And I divide them."
Deus ex Machina: A literal example with Rose, (well, technically it would be Ex Machinam, since it's coming out of the machine) a mere human companion, opening the heart of the TARDIS (although with help from her mother and Mickey), to telepathically pilot it to the 2001st cenutury to save the Doctor, absorbing the vast energies of the time vortex, emerging out of from the TARDIS as the "Bad Wolf" to save the Doctor from the Daleks. "The god out of the machine".
- There's also the Dalek Emperor, who has come to think of himself as a god, due to having recreated the Dalek race as he saw fit.
- And both examples were executed with the requisite A God Am I speeches.
Decoy Protagonist: First-time viewers who haven't been spoiled could be forgiven for seeing the title, seeing Lynda's role in the story and thinking it means that she's going to replace Rose.
"Facing the Bullets" One-Liner:
"EXTERMINATE!"
"I kind of figured that."
Foiler Footage: An alternate ending where Rose dies was filmed with the intention of screening it for critics, but Davies decided it was too inferior to use.
Go Out with a Smile: Nine
God Emperor: The Dalek Emperor.
A God Am I: Bad Wolf has shades of this.
The Doctor: It's not right! You can't control life and death!
Bad Wolf: But I can.
- Also the Dalek Emperor: "I reached into the Dirt and made new life. I am the God of all Daleks!"
Heroic Sacrifice: Several.
I Will Fight Some More Forever: Jack continues firing his pistol at the Daleks as he's backed into a corner. "Last man standing!" Finally, they've got him, and he spreads his arms in a "bring it" posture.
If We Get Through This
It Has Been an Honor: Played with.
The Ninth Doctor: You were fantastic... And d'you know what? So was I.
Kill 'em All: Virtually everyone on the station is slaughtered by the Daleks (who seem to sustain exactly one casualty before Bad Wolf unmakes them), and Captain Jack is the only one who seems to be restored to life. Only one person on the station doesn't die, and that's Rose. Granted, the Doctor and Jack get better, but they still die. And that's not even mentioning the offscreen deaths of potentially billions of humans on Earth, which the Daleks are bombing (we see entire continents distort from the blasts).
Lip-Lock Sun-Block: The Big Damn Kiss between the Doctor and Rose.
Love Triangle: The Doctor, Jack and Rose all kiss in this episode.
Morton's Fork: The Doctor doesn't have the time to refine the delta ray—either he lets the Daleks live and puts the whole universe at risk, or he commits another act of double genocide and takes out the human and Dalek races at once.
My Skull Runneth Over: Almost happens to Rose, so the Doctor absorbs the energy and blocks her memory.
Bad Wolf: The sun, and the moon. The day, and the night. But why do they hurt? ... I can see everything. All that is. All that was. All that ever could be. ...My head... is killing me.
Not Me This Time: The Doctor, after the battle starts, assumes that since the Daleks seemed to be behind everything else that were behind the "Bad Wolf" words, asks the Dalek Emperor why he spread them through history. The Dalek Emperor responds that he doesn't know anything about them, and the Doctor realize that if the A God I Am Emperor did do it, he would have gloated about it like he did with the rest of his plan.
Physical God: The Bad Wolf/TARDIS Matrix/Rose
Reality Ensues: Lynda with a Y. The Doctor thinks she'd be a great companion and even likes the idea of her travelling with him, but when you have a Dalek Empire descending on the station... what do you think will happen to her?
Retroactive Recognition: Lynda's actress, Jo Joyner, would join EastEnders not long after.
San Dimas Time: Pointed out by Mickey when Rose is desperate to get back to the confrontation that's happening right now...198,000 years in the future.
Sacrificial Lamb: Lynda, whom the last couple of episodes seemed to be setting up as a possible companion.
Scary Dogmatic Aliens: "DO NOT BLASPHEME!"
Shaggy Dog Story: The elaborate battle plans and heroic resistance that most of the episode focuses on hardly even slow the Daleks down. Earth's bombed enough to reshape entire continents, everyone on the station apart from the Doctor dies in a one-sided massacre and the Doctor can't go through with destroying the rest of humanity to stop the Daleks. Only Rose's return saves the shaggy dog from getting shot.
Shout Out: "The Parting of the Ways" is also the title of a chapter in Harry Potter and the Goblet of Fire, the film version of which also featured David Tennant, as a character whose last appearance was in that very chapter.
The So-Called Coward: When faced with destroying all life in the system, he'll choose coward over killer any day.
Space Is Noisy: Chillingly averted. When the Dalek rises up to the window of Lynda-with-a-Y's hiding place, while you don't hear it, its dome-lights flash in what is clearly it shouting "EX-TER-MIN-ATE", before it blasts the window apart, opening the room to the vacuum of space (evidently, the Daleks say it more for themselves than anyone else at this stage).
Stable Time Loop: The Arc Words "Bad Wolf" were planted by the TARDIS-possessed Rose so she could figure a way to get back to the Doctor, which involves Rose getting possessed by the TARDIS so she can plant the "Bad Wolf" messages.
The Tape Knew You Would Say That: In the Doctor's holographic message to Rose, he turns his head to her as if he knew she would walk around the hologram to its side.
Technobabble: Try saying that while drunk.
You Shall Not Pass: Cap'n Jack!
Wham Line:
Dalek Emperor: "I did nothing...They [The Bad Wolf message] are not my design. This is the truth of God."