I've never read a game-to-book adaptation. I expect them to be crap or mediocre, with wooden characterisation and predictable plotlines. Nonetheless, someone I know reads them, and is pretty impressed by Warhammer 40k books in particular - though that's a tabletop game.
Knowing me, I'd keep thinking the book is a game, and get frustrated at the lack of gameplay. GRRR just let me play the goddamn game! *squeezes book like a gamepad*
Then there's the whole argument about the purity of a storytelling medium. Books are the purest medium, trying to transfer books to films or games is going to water them down somewhat. Trying to reverse-engineer games or films into novels may result in crappiness, as what looks impressive as a game plot may turn out to be complete fanwank on paper. There are exceptions, though, and I respect that. This is not to rubbish game storywriters, either. It's often that a lot of books based on games are cynical corporate merchandising, and are not the creative output of the original storyteller.