I love wide angle lenses. My kit will always have one of at least 20mm. When I used a digital camera (Sorry for swearing ) I bought a Sigma 15-30 and it was used for most of the time. When I went back to film it was a real killer! Although not the sharpest of lenses open wide, from about 5.6-8 in all focal lengths it is superb and gives me so much more scope for what I like doing best in my style of photography.
However with a wide or super wide I find that you have to watch out for the verticals, distortion, getting your feet in the shot and with a low sun getting your shadow in too. They are an acquired taste but go for it. The Zuiko F3.5/21mm is a cracker as someone has already said.