We reported of the sequel to Jules Verne's popular novel game not too long ago, and Chillingo reported it as one of the biggest games in the App Store along with this game being another AAA title. While I'm not a huge adventure game fan myself, fans of Myst and Secrets of Monkey Island should feel at home with this one.
First of all, I would suggest you start deleting the games you don't play or clearing up some space. Secrets of Mysterious Island takes up a whopping 704 MB, and at the time of download that size should double. If you aren't able to download the game, you'll need atleast 1.4 GB to start up the process.