Fine!
Have done some more driving, on my second tank of fuel now!
I'd say while it's clearly faster than my tuned 335i... it does what it does with much less drama. It's quieter, so stable and composed like it's not even bothered when you're flooring it or slamming the brakes. I floored it in a countryside intersection and did a small drift, I was definitely a little sideways but I couldn't even hear any tyre squeal. Perfectly smooth, most mellow feeling drift ever. Maybe the fake interior engine noise was hiding the tyre sound. I guess if I imagine myself driving the 335i hard, making a lot of noise, spinning tyres, slamming the brakes... the M4 would casually keep up without breaking a sweat or making much noise.
It's so insulated, you can see why they added the fake engine noise. It's the only way you can tell what the engine is doing unless you have the windows down. At least with the stock exhaust, because it's not that loud. I think I'd want an aftermarket exhaust or downpipes before I disabled that (which I'm not doing any time soon).
I also don't get why some people online complain that it's constantly trying to kick the back out. I think these guys just drive with the assist on and assume every time they see the TC light come on it's just stopped them from throwing the tail out.
I drive it around in MDM (from what I understand, it means assist only kick in if you go beyond a certain slip angle). Even with foot to the floor on imperfect roads I never had any unintended sliding, just on one slippery wet bit of road it struggled for traction from a standstill. Maybe my opinion on this will change as I get more confident with it, I'm still taking corners very carefully - both because I haven't driven in 6 months thanks to the situation with my old car and I'm still getting used to the M4.
Speed builds up both more quickly and smoothly than the tuned 335i, it's even easier to get into loss-of-license territory when overtaking. I performed what felt like a slightly aggressive overtake on a country road of a single car, who was doing 90, and I hit 150kph as I was going past the guy... it barely felt any different to 100kph.
Think the same effort in the 335i might have me hitting 130... at least then I might keep my license if I get caught doing it!
The HUD is also great, seeing your gear and speed without having to look down is actually super helpful when driving a bit 'spiritedly' on the back roads.