Yup, I can only echo what others have said: This is so far the best Ninth Doctor NSA Book!
Out of the first three books, this one has easily the best Characterization for both Rose, Nine and some other Character surrounding them. It also feels like the best Attempt to translate the Style of RTD1 to the Page, which can be a good Thing for the People, who want those Tie-In Books to actually *feel* like a Tie-In. (Admittedly I was a bit more interested into the almost 'classic'-Approach in the first Book, due to my own Preference, but that's besides the Point).
As always reading Rayner's Prose is as pleasant as always, having read her other NSA *The Last Dodo*, I noticed that her Writing in the NSA are easily some of the most pleasant ones.

I think the Premise itself is not too much to write home about. Don't get me wrong, I think it's a lovely Idea (even if it very much screams of a 2000s Story), but one that has been done in plenty of other Mediums. That said, I think Rayner does a great Job regardless (for the most Part).

Despite some Issues (the Supporting Cast was one of the weaker ones, some Parts of the Story feel rushed), I enjoyed it throughout. Hopefully the other ones while be as enjoyable or even more so!

On an unnecessary Side Note, but I think this one has one of the very finest titles for any NSAs!