Good lord, the Slitheen were originally going to be in The Impossible Planet? (Imagines this for a minute....)

Dodged a bullet there, then. All hail The Ood!

I assume they were RTD's input to the story, as he's credited as their creator despite not being credited as writer of TIP/Satan Pit...

Love and Monsters or Robots of Sherwood. I can't really decide which is worse, I just recall that both were so bad that they don't deserve to be called Doctor Who episodes (or even stories really), and I don't care to watch either of them again to decide which was worse!

Love and Monsters
Fear Her
Night Terrors
God Complex