This is a good novelisation of the TV story, and manages to keep a lot of the original darkness and bring it to the page. Maureen o'Brien does a wonderful job of narrating this - she reads the story so well, the characters sound clearly defined, and honestly I might imagine her voice instead of Lindsay Duncan's doing some of Adelaide's lines now!
There's not loads and loads of new things in here that aren't in the original, but there's some nice extras. We get some expanded backstories, a cool new bit with an ancient Mars relic from the Ice Warriors, as well as a prologue detailing the history of the Flood. (Although - I'd always assumed that's just what the Doctor called them! But it makes sense for the novelisation for it to become their Real Name.) The new aspect that works less well is the flashback to Adelaide's encounter with the Dalek. It starts with her away from home, camping, and involves her having to get into a stranger's lorry with some friends to make it back to London! It's honestly a bit of a bizarre choice, and though I get what we're meant to be learning about her character, it's a decision that made me feel quite uncomfortable, really.
The story itself is told really well, though. The biodome is slightly reimagined to become more Martian, which is nice, but the very creepy imagery of Andy and Tarik from the original is moved from a dark, shadowed path to a clearing, which I wasn't quite sure about. The description of the Flood-possessed crew is really scarily done, and there's a real sense of dread as they are taken, one by one. Hearing this book as a novelisation really emphasises how dark the story is, and makes it feel more real.
The 10th Doctor is characterised well, and pretty much as he is in the episode, but there's a little more exploration of his turn to becoming the 'Time Lord Victorious'. I did wonder if some of the more extravagant edges of the character, and of his arrogance, are softened a little bit here? We're maybe led to be slightly more forgiving of him over Adelaide's fate than we should be? I think Adelaide's fate isn't dealt with to the extent it could be... but maybe that's for the best? It's a very intense story, and therefore at times a very intense novelisation, and it's maybe not one Doctor Who can do very often. We're given the Doctor Who version of events that are not really very Doctor Who-y, but this novelisation keeps up the sense of dread really well.