I'm not very good at hiding what I feel either, and I used to be super insecure about that, but ever since I had to take on a leadership position at work and it became useful I've kind of gotten more accepting of it. Apparently I send a lot of non-verbal signals that are helpful in cuing other people. And while I think that being able to hide my feelings better would make me more mysterious and elegant, I think it'd also make me less approachable and less open, and people say they like those things about me because they make me seem (which I am) very accepting of others. Because of this others feel comfortable sharing their hopes and dreams and fears and passions with me, and that's so valuable to me. It's like my lifeblood. I can't imagine life being nearly as rich or meaningful if people didn't share those things with me. I just try to make sure that I express my feelings fairly according to the situation, and don't hurt people unintentionally. Sometimes at work I am aggravated, but I try to analyze the situation to ensure that I am aggravated with the accurate person for doing the exact thing that created an injustice. And more and more lately I try to channel that aggravation into standing up for myself and others, instead of just venting it everywhere. Trying to use it productively, you know?
As a related aside, I just read that there is some evidence that depressed moods can be especially conducive to increase creativity. So next time you're sad... might want to try breaking out some sad music and some colored pencils or paints or yarn or whatever and go to. I'm going to try this, too. I figure it's better than wallowing, at least!