Lots of people come here and ask these questions. We don't have a firm answer because we all not car expert like The Stig.

But here's my 2 cent review after driving 6 months.
First, won't tell you about the specs. You can find them in Net or SA so, skip that.
a. Driver POV
If you drive those mass production cars like Civic & Altis, you feel M3 a bit different. Different in terms of how you fit in the drive side. Buttons and other important stuff are easy to reach. Speedometer, MZD, panels are very close and doesn't requires you to move more to reach. Just sit like a robot and can do anything.
b. Passanger POV
Sitting on front driver seat also feels the same as driver. All are within reach. For back seat passanger, you will feel crampy especially you are more than 5 feet 7'. This is because the seats are design for "vertical" feel and not like Altis, where you can recline, this one quite stiff. Also, the rear window is relatively small, can be a problem for those have that dunno-what-it-called phobia. Despite longer wheelbase, the rear can best fit 2 adults and 1 children. If you fetching 3 adults, this car don't really fit for long drive.
c. Handling
A lot of people might confuse with handling. Because Altis also claimed that their handling is good. Even other lower C-segment car also claim their handling is 4/5. But why people say M3 handling is good? Answer is cornering. You can feel much in control in cornering and felt the directions of the wheels. Others claim thier cornering is excellent, but you have to try M3 yourself. Only other that have good handling is Ford.
d. Performance
M3 is not the best performance here in low end. You feel sluggish in low end. (Mainly acceleration) But you do feel the power in mid to high end. This is because the Skyactiv GB which mimics the CVT and DCT concept. CVT has always know to give seamless transmission and save fuel. When I'm driving at low end (meaning minor press on acceleration) I felt like driving a CVT GB. When you drive at mid to high end, then you feel the power (Can't comment on DCT because never drive before) However, I agree with some reviewers in Youtube. The Skyactiv GB kinda "lazy" to shift gear. When I felt low power, I switch to "manual" via paddle shift. This is where as I shift to manual, the GB already shift to low gear, and using paddle shift, means drop lower gear. Thus, be careful of shifting manual, advise to use the stick for manual than paddle shift.
e. Maintenance
So far, can't tell how much maintenance is and cost. The disadvantage here is currently, no suppliers to provide the parts. All from Japan. Good thing is at least the parts in Japan means more durable than local. No?
Overall, bear in mind this car is claimed to be build from scratch. It's not benchmark with other C-Segment cars. It just to achieve efficiency, power and fun to drive. This car is more for people towards performance and fun to drive. Something that defy convention.

If you looking at family sedan, write this one off...
hehe nice one..... but i bought this as my family car..cause 2 adult 1 child..so ngam ngam.... if focus is too cramp at backend... i think if only couple or lone driver focus is a nice drive..else this is a better option unless comparing with altis and civic with large backseat space...
so far bm and merc, their drive panel has changed (those knob controller). so far only m3 moving forwards but the rest still old way of functioning...