I completely agree... It's the only reason I don't like Unbreakable as much as I should--it's an absolutely incredible film, but it's just too dark in every way. The subject matter is pretty intense, the conflict and surprise ending is just disgusting (in a brilliant way), and there's only like 3 scenes in the entire film where the scene is actually brightly lit. Every time I think of Unbreakable, the first images that come to mind are of Bruce Willis standing beside the pool in his cloak under the pouring rain... Sure, it's a triumphant scene, but it just looks so... depressing.
Signs has always been at the top of my list because even though it's absolutely terrifying, it's also incredibly funny in all the right places--it has tons of much-needed comic relief. And the ending is just so uplifting and satisfying. LITW is my #2 for the same reason. Not scary, but the tone of the entire film is very happy and you feel like the movie is very complete at the end--like Signs. I don't get any of that with Unbreakable.