Lord of the Rings - The only tampering I recall at the moment was the battle of helms deep: there were not elves in that fight, but peter jackson did a pretty good job adding them in
I could name dozens of irritating changes made in this movie, the elves at Helm's Deep just being one of the most horrible, drastic examples. That's missing the point, though - I may not like the particular changes that Peter Jackson made, but I agree that changes were needed (and I deeply regret that he didn't
change that multiple endings thing).
That's the thing about adaptations, you see. A film takes on average two hours. The average book, once you cut out the descriptions (which in a movie are, of course, visualised)... still takes at least four to six hours. So how can you turn it into a movie without making changes? The same goes for games, except that here changes are needed even more. Let's forget Wing Commander (which was actually a fairly easy game to convert) for a second. Let's talk about, say... <draws a name out of a hat> Super Mario Brothers.
So... the game has no story whatsoever
. It's about a guy that walks sideways through dozens of screens, jumping on top of turtles to kill them. Convert that into a movie without making any changes... and you get a movie about a guy that walks sideways through dozens of screens, jumping on top of turtles to kill them. Oscar-winning material, that's for sure
. And not only will it suck as a movie, it won't even appeal to the people who played the game, because what appeals in the game is that you control the guy walking sideways
. You really can't do that in a movie, so you're left with very little indeed...