A game that doesn't let you break out of the original plot is just a bit of an animated storybook in a way, but if it does, it's not true to the original book. In the long run, games must adhere to the spirit of the material, not the letter, or they;re just going to suck. And any hardcore fan who screams about it not adhering to the letter probably doesn't "get it".
A lot of people who rail against copyrights aren't against the theory of copyright, but the practice. It used to be that copyrights lasted around as long as patents, now they last the lifetime of the creator plus another seventy years. Isn't 7 or 28 years long enough to profit on a movie, book, etc.?
Additionally, the ideas of fair use, being able to make backups of the stuff you buy, not being locked into a format, etc. are all being chipped away at by law, contract language, and DRM.
"Confound these ancestors.... They've stolen our best ideas!" - Ben Jonson