One small correction here:
"The Skyactiv engine also gets an impressively high 12:1 compression ratio (about 20 percent higher than most engines) to help get the most power out of every drop of regular unleaded fuel, while a specially-tuned 4-2-1 exhaust system helps fight the engine knock that can otherwise be the Achilles heel of high-compression designs."
If I am not mistaken, Mazda could not implement the 4-2-1 exhaust manifold in this application because of space restrictions. Hence, they had to drop the compression to 12:1, whereas in the CX-5, the same engine has a 13:1 compression ratio.
The issue I found in the 3 is rear seat space. I found it very tight when compared with my 2002 Protege. I can comfortably sit behind myself (6 ft) in the Protege but found it a challenge in 2010+ Mazda3s.