While this isn't my favorite lens (that would be the Olympus 45mm/1.8), this is currently a very close second. This is an excellent lens, especially for low light. The only reason why this isn't my favorite lens is that for my particular uses, the 45mm is a more useful focal length. For most people, however, the 25mm is probably a way better focal length. I don't believe you can get a faster lens than this one at such a low price.
The Good Parts
* Inexpensive at just over $200 * Good all around focal length for most people * Sharp and good color * Metal mount * Fast F1.7 aperture means you can use a lower ISO in low light * Good AF speeds (your mileage will vary, depending on the camera you are using) * Comes with lens hood * Lightweight * Good bokeh * Well made
Could Be Better
* A little chunky (volume-wise, it's bigger than my 45mm)