The problem with the first installment in the Usbourne Puzzle Adventures is that the key concept of the series (and the gist of the story) is not properly explained. All of the books in this series are a blend of mystery and adventure, with plenty of reader interaction due to the presence of questions at the bottom of each page, challenging the reader to figure out a code, maneuver through a maze or find clues in the illustrations that will lead them to the natural continuation to the story.
The problem with "Escape from Blood Castle" is that it is not specifically clear on what the protagonist is trying to achieve, or how he relates to the other characters during the course of the story. Subsequent books are very clear on what their objective is: find the buried treasure, catch the bad guys, discover the secret civilization, etc, but "Escape from Blood Castle" begins with: "Ivor couldn't let himself be cheated of wealth and title by his creepy cousin." That's all the back-story we get. Who his cousin is, or who Ivor himself is, and what he's trying to achieve by breaking into Blood Castle isn't clearly explained.
It eventually becomes apparent that Ivor is after a will, and that "cousin Boris" is in fact an impostor, but the main thread of the story is unclear throughout. The fact that a portion of the story is told in the "answers" section of the book shows that the narrative really needed to be better thought-out. Furthermore, some of the puzzles are frustrating: in one, for example, you need to mark the passage of a pinball machine ball to make it add up to 208, 361 points. Huh?
Likewise, I'm not entirely fond of Graham Round's illustrations; he's done excellent work in The Curse of the Lost Idol (Usborne Puzzle Adventures) and Danger at Demon's Cove but here, the house and Ivor's eccentric family members come across as creepy and grotesque. Of course, maybe that was the point, but it didn't really appeal to me.
All in all, not my favourite Usbourne Puzzle Adventure - and since there are so many out there that are entertaining, spooky and coherent, I'd suggest skipping this one and tracking down others.