I've played the heck out of this game, which is all well and good... however:
I've noticed that in solitaire on Merlin difficulty, it's easy to immediately see from the layout of cards and the cards that are drawn whether the game will be possible to complete. To that end, a major part of finishing books ends up being an immediate resign/restart cycle.
I feel like the game would greatly benefit from two things:
The ability to replay a game. If I've got a layout that I think is doable, and I make a mistake halfway through, it would be nice to retry the same layout.
Story mode, featuring a specific set of cards and companions that is definitely finishable and preferably plays out similar to the books.
Otherwise - great game!