Please don't take the Amazon star rating too serious - every lens has its pros and cons that I wouldn't want to squeeze into a single one-dimensional figure...
A quick note about me: I have been into SLR cameras and lenses for more than 20 years - as a hobby in the beginning and professionally later. Maybe because of my technical background I started testing my own lenses quite a while ago. I have a (no longer so) little test lab of my own where I do 6 different image quality tests (after taking a lens out for a while).
The EF 28mm f/2.8 IS USM is a compact and well-built prime lens with a common wide-angle focal length, a good maximum aperture and a modern image stabilizer that compensates up to 4 f-stops. While the image stabilizer sounds great one has to consider that it's not as necessary in wide-angle lenses as it is in telephoto lenses - but I still appreciate it. The lens is best used indoors or for architecture and landscape photography. When using the lens with an APS-C camera the resulting effective focal length of 45mm is close to a standard / normal lens and thus can be used for a whole variety of things.
The lens offers good image quality - sharpness is great straight from f/2.8 and there is only a small amount of barrel distortion visible. My lab tests have shown that color fringes ("Chromatic Aberrations") both in focused parts of the image ("Transverse CA") and in out-of-focus areas ("Axial CA") are visible but compared with its immediate peers the lens's performance is quite respectable. There is no curvature of the focal plane ("Field Curvature") but corner shadows ("Vignetting") are very intense and they are visible even stopped-down.
The EF 28mm f/2.8 IS USM is similarly priced to the
EF 24mm f/2.8 IS USM but costs a lot more than the
EF 28mm f/1.8 USM which offers an even better maximum aperture (which is great for available light photography) but lacks an image stabilizer and cannot compete with the EF 28mm f/2.8 IS USM's good image quality.
Chances are you already own a zoom lens covering the same focal length in which case you are probably most interested in the EF 28mm f/2.8 IS USM for its good image quality, compact size and the maximum aperture of f/2.8.
Is this lens for you? I think it really depends on how you configure your kit. If you have use for the focal length / aperture combination the EF 28mm f/2.8 IS USM's rugged build quality and good image quality will leave no regrets.
A much more detailed review of this lens together with all test shots, sample images and technical data is available on my website LensTests_com.