Some call it the "fantastic plastic" and given the build quality, you'll know why. The Canon 50mm f/1.8 II is the lightest lens you're likely to ever hold in your hands (except for maybe the lens baby); the lens cap is laughably small, the focus ring is too! Also, it's autofocus is quite noisy and doesn't perform well in low-light or low-contrast conditions at all.
This lens is quite sharp and for the money, it can't be beat. If you even THINK you might have a use for a fast normal prime, it may be worthwhile to check this lens out!
Here's a link to my sharpness test results for this lens.
Here's a link to my sharpness test results for the Sigma 30mm f/1.4 (around $400) for comparison.
And here's a link to all of my lens test results.
In the real world you aren't usually taking pictures of black and white text. I do my testing this way to show minimal differences that would probably never be noticed on actual photos. Also, remember when viewing the test results at 100%, this is the equivalent of having your photo printed at 30x20. If you don't crop much and don't print that big, you don't need a lens that's perfectly sharp at 100%.
...In the past few weeks I've been using this lens for studio photography, pics of my fish, etc and I must say that it's definitely a workable lens. If your subjects are moving (like my fish), you'll have to focus manually with that tiny little focus ring, but for me it really didn't matter. I got used to it pretty quick. In fact, I almost feel bad that I spent the money on the Sigma 30mm f/1.4 -it seems like a waste when this lens is so close in focal length and quality (of pictures). The Sigma is definitely better built, but I don't think I'd ever be able to tell the difference in quality between the two if real world photos from them were placed side-by-side. If you're deciding between the two and you're willing to live with the downsides of the "Fantastic Plastic", I'd say go for it!
What do I mean by "Prime"?
Prime lenses are non-zoom lenses, so they stay fixed at one focal length. If you want to "zoom in" or "zoom out", your only option is to do so with your feet.
Why would you want a "Prime" instead of a "Zoom" lens?
In the old days primes were considered superior because zoom lenses were often poorly made. Technology has since improved and some zooms are as good as primes. Zoom lenses, however, cost more (sometimes MUCH more). So, these days people usually buy primes to get a better quality lens for a lower price. Besides, "zooms" are not usually needed for studio work, macro photography, etc.
What do I mean by "a Fast lens"?
Fast lenses allow you to get higher shutter speeds in low-light conditions without a flash. Most of the time they are used to avoid blur in indoor photos when you can't (or don't want to) use a flash.
How do you identify how "fast" a lens is?: Lenses are identified by their focal length (for this lens, that's the 50mm part, which tells you how close your subject will appear through the lens), followed by the maximum aperture of the lens (for this lens, that's the f/1.8 part). The lower the number that follows that "f/", the "faster" the lens is (or the better it will perform in low-light conditions). f/1.8 is VERY fast, although my Sigma is a f/1.4 and Canon makes a 50mm "L series" lens that's a f/1.0!