After all the speculation as to who the titular daughter was going to turn out to be, what we in fact got in The Doctor’s Daughter was a new character – an extension of the continuity rather than an attempt to weave a story within the established history of the programme.
As an episode it wasn’t bad – although the plot somewhat fell apart when it got towards the end with the idea of the war only having been going on for seven days – especially when you took a look at the human general. However, the basic premise of Jenny being created and the chance to explore how the Doctor dealt with his new family tended to rise above the holes in the plot. Perhaps the only part that felt really unnecessary was the scene where Martha falls into the quicksand and is saved by the sacrifice of the Hath who is accompanying her – it would have made more sense had it been seen and used as an example to the warring humans and Hath, but taking place as it did away from the main action there didn’t really seem to be much point, except maybe to remind Martha of the cost of travelling with the Doctor and why she stopped before.
To some extent, Martha seemed to be present primarily in order to give the Hath view, as the character of Donna was needed to counterpoint the reaction of the Doctor to his new, and potentially rather violent daughter. Alongside this, as his daughter, Jenny was able to challenge the Doctor on some of his own actions when they appeared contradictory in a way that other characters maybe cannot – in particular his criticism of what she was.
Ultimately though, what the story gave us is another Timelord in the universe (and perhaps a character designed to appeal to another audience demographic) – and from the comments at the end of the accompanying Doctor Who: Confidential, that were as close to spoilers without actually giving away the upcoming plot – one who we are going to see again before too long.