Well I've been a fan of Doctor Who since David Tennant started as his light hearted approach to enemies always cheered me up in sadder parts of the episodes, not that I don't enjoy the drama it's just that too much down and dismal talk can be depressing. I always did like Rose Tyler as she could bring a lot of feeling to the episode but I think the Doctor needed something more, someone who was in it to be a best friend instead of something more. I see Donna and the Doctor as siblings rather than lovers. Bringing Donna back was one of the best moves of the series, I couldn't endure another series of Martha flirting with the Doctor in every single episode! I think this episode was purely for the meeting of the Doctor and Donna as the Adipose plot was not a hugely interesting or exciting one but I think if it was all of the attention would be drawn from the excellence which is Donna finally finding the Doctor again. My favourite part was probably when they say each other. Catherine, who is obviously known for her comedy sketch show, has always been great as Donna and made me laugh very much when miming to the Doctor through the door. Also, as someone else has said, adding in the lines about the Doctor just wanting "a mate" and Donna mistaking it for something else and becoming offended was needed to show anxious viewers that this series was not going to be another 13 episodes of flirting.
Review of Partners in Crime
