I saw the Princess Diaries (only the first one) and thought it was all right, but I don't know anything on the original work so that opinion could always change.

Eragon, though.... The experience was like "OH MY GOD, STAB MY EYES AND BURN MY BRAINS OUT PLEASE."
In fact, I didn't allow my boyfriend to watch the DVD even though I was the one who turned him onto the books. It was the worst movie I've ever seen, and I've seen many movies. Oh God, I'm ending this comment now before I blow into full rant mode.