In my opinion, the "Kai" design is more of an evolutionary step rather than a revolutionary one from the outgoing "Kodo" design.
From Motor Trend:
"The Kai Concept rides on the latest iteration of Mazda’s Skyactiv platform and measures 174 inches long, 73 inches wide, 54.1 inches tall, and has a 108.3-inch wheelbase. This makes it 1.6 inches shorter, 2.7 inches wider, and 3.2 inches lower than the current-generation Mazda3, with a wheelbase 2 inches longer"
http://www.motortrend.com/news/mazda-kai-concept-previews-next-generation-mazda3-in-tokyo/
I'm I excited?
Yes
Do I think it looks amazing?
Hell Yes!!!
When I saw the pics, did my heart felt with joy?
Yes! Since I love Mazda and many of us love the brand!
Completely stunning! Mazda is doing things so well in regards to the designing of their cars, their future line-up will definitely be a stunning one! Have you seen the Mazda Vision Coupe? (Most probably the new design for the Mazda 6), Spectacular!
My only critic right now would be the rear part of the vehicle as it looks quite small, but we'll have to wait and see how much of this concept design will actually be transferred when the actual production of the 4th Gen 3 begins!

(No Brembo brakes for sure lol)