I have to agree with most of the other reviews out there, the EF 50mm f/1.8 has a very cheap build quality. It's a totally plastic construction. In fact, I guess everything but the lens itself is plastic. So yes, the build quality is cheap - but so is the price. Even at good well-known places, this lens can be had for around $70.

Looking at the plastic lens, considering the price, touching it (it's only 4.6 oz = 130g), one would never expect it being that sharp.
Its motor to auto-focus is not among the quietest and fastest but one would never expect it being that sharp.
F/1.8 make it a nice lens for low-light and indoor use, but one would never expect it being that sharp.
Zoom lenses are really versatile but this Canon prime lenses is so inexpensive, light, and small and ohhh, did I mention, one would never expect it being that sharp.