Have used my friends for a month (we traded I have an M3) and it's a great car! So many complaints from critics, but the trick is that you really have to tinker with the settings first. Everything is programmable. Set the M mode to everything power and it's frighteningly fast.
For people who complain about the stability control not being able to fully disengage, you're testing the car in a controlled environment. In a real world setting, a car with this much power and this much mass needs it to be on. Steering is a bit numb however.
Sound system and idrive are a big upgrade. Styling is still understated. Seats are very comfortable. Overall great car, but still love my M3.