Strictly speaking, BMW's new M135i is not a genuine M-car. Being an M Performance (rather than M-for-motorsport) model, it has some serious performance tweaks but stops short of being a hard-core road-racer.
In my opinion that makes it one of the most worthy M-machines ever, because it's very close to the spirit of the model from the M-division that started it all.
That model is not the M1, by the way, if you'll excuse the sacrilege. True, the exotic mid-engined M1 of 1978 was the first production model from the newly formed BMW M GmbH (1972), but it was really an anomaly.
The M1 project was originally outsourced to Lamborghini (but had to be finished by the Germans - sound familiar?) and intended purely for racing. But by the time it was finally ready, times and racing series had changed, and the best option for competition was a support series for Formula One called Procar, which was based on series production models. That's the only reason the M1 was ever built in road-going form, and BMW M hasn't built anything like it since.