Admitedly, I've only had it for 1 week after trading in my '08 4.8i last weekend.
Drove a 5.0i right before the M, left with the M.
First impression is that it is fast; really, really fast compared to the 4.8i. The power is immediate and endless when you dip into the throttle.
Steering is quite different from the non M.
It's lighter at low speed, tighter at higher speed, wonderful all around.
Suspension is tight when it needs to, very compliant over bumps too.
Overall, a massive upgrade from my prior X5 and absolutely awesome!!
Lots and lots of power.
It takes off and doesn't stop.
New iDrive is much better.
Love the HUD, especially in M mode.
Needs ventilated seats with the cinnamon interior.
Ain't cheap either, but less expensive than the Porsche Turbo by a lot!