Take the scene in Moria. The phrase "Ai! A Balrog!" works perfectly well on the printed page, but spoken? Naaaah. So what's the alternative? A good actor who knows how to show emotions in an understated way. The sheer terror on Legolas' face when Gandalf talks about the Balrog shows how bad this threat they're facing is. Legolas is several thousand years old, and has undoubtedly faced many terrible enemies, and yet he's terrified at the prospect of this particular beastie? He didn't need to say anything, the look on his face said it all for him!
Bottom line: elves don't show their emotions, except in extreme circumstances. I'm glad they're portrayed that way in the movies, because that's how it's supposed to be. [/rant]