This is the first Doctor Who book I've read and it was about what I expected - as a book, it's not very good. The writing is very simple so basically anyone over the age of 8-10 could probably read this. As far as the "episode" went, the Doctor was like the Doctor for the most part. There were certain lines I could imagine David Tennant saying. Martha was Martha, yet she wasn't. Personally, I've never liked Martha to begin with, she's easily my least favorite companion so as far as her character's concerned, I can't really think of much that defines her as a person. In this book, she could've been anyone, really. She did companion-type things that all the companions do (listen to the Doctor, then stop listening to the Doctor in order to do something she thinks is right, etc.), but there was never any moment when I thought, "Oh yes, that was a very Martha Jones moment." Maybe it's because I'm not a huge Martha fan, but I'm not sure.
As far as the story goes, at first I really was intrigued both by the ship & the forest. By the end, however, I was both a little bored and confused. I'm not sure if it's the writer's fault for just not explaining well what happened or if the story itself just wasn't very good, but while I did get the gist of what was going on by the time I reached the very end, for the last 70-50 pages, I spent a lot of time thinking, "What is going on? How does this all tie in?"
Overall, it's not terrible, it was still a fun read and if I'd given myself enough time, I probably could've finished this within a few hours.