After looking at the cars for the last 24 hours, here are my initial thoughts..
I don't like anything about the M4, but that may be due to the color. I love Sao Paulo Yellow, but I don't think it looks good on a big bulbous coupe. I think it would work better on the M3 where the novelty of having a bright highlighter color on a big sedan is fun.
I like the M3 except for the front end and this portion of the car:
I get that they wanted to use the same doors as the regular 3er, but I think it could have been done more gracefully.
And finally, I think they nailed the interior, but would have liked to have seen a real parking brake.