Had a drive in an M2 this morning having jumped straight out of my M135i and whilst the car definitely felt much more connected than mine I was a little underwhelmed by it's straight line performance, which is all I could test on the open road. Above 5K RPM it seemed to have a bit more go than mine but otherwise there was very little in it (unsurprising really).
The brakes, however, were much better. Much more immediate and better feel, and in combination with the wider tyres it will out-stop an M135i/M235i pretty comfortably I'd expect. The ride is sharper and you definitely feel more through the rear of the car than in mine. It had a manual gearbox which was fine, but the clutch was SO light I struggled a bit with it to begin with. I'd definitely order the M-DCT (which is what the previous owner changed it for apparently).
I imagine it would be an absolute hoot on track, but I'd definitely be wary of spending £50K on one for daily use. From inside the car there's basically nothing to distinguish it from mine, and therefore I don't think it feels like a £50k car ought to for most of your daily driving. There are no options available for it that you can't get on the M240i for example.
All that said, the one I drove had done nearly 19k miles and the dealer wanted almost 40K for it. That's pretty decent value retention considering this particular example was ~£45k new.
Also whilst I was there I asked (out of interest) about the new 5 series, and the dealer told me that they are selling more petrols than diesels so far, and more 540i than 530i as well so Fox, there's hope for you yet!