I've heard some good things about this lens. I've also heard some not so flattering things about it "not being sharp", and I suspect, based on the people I've heard the not so sharp comments from, that they shot it at f/1.8 quite often; this lens design has a very prominent "haze" issue at f/1.8, which a LOT of lenses do, something called
veiling glare, where the image is sort of sharp, with a veil of haziness over the top...that is a really,really,really common issue among many lenses when they are shot wide-open. Again, a LOT of lenses have veiling glare wide-open, and this is something that has been noted on many lenses for the past eight decades, but in this, the internet era, there are many people who are fricking clueless, and will often shoot everything at f/1.8, looking for "bokeh"...and they get on the internet and complain...
This review has a lot of practical information about the lens.
Canon 28mm f/1.8
You need to keep in mind that this is a moderately-priced lens, which sells for around $300 on the used market, and the new retail price is under $500...in this, the 15th year of the 21st century this is NOT a high-grade lens, especially for a wide-angle lens. Wide-angle lenses that perform extremely well are often expensive. Wide-angle lenses often show very pronounced optical defects, compared against normal and telephoto lenses. The newer a wide-angle lens is, the more likely it will be a good performer on digital. FILM-ERA wide-angle lenses are often substandard on today's digital sensors, compared against older, 1990's-era wide-angle designs. At wide f/stops, wide-angle lenses that perform very well are typically new designs, and expensive. Newer designs are often better than higher-priced but old designs.
Bottom line is--this is an inexpensive lens. It is what it is.