Me too, but I'm biased.
I own two TREKs though I shopped for other bikes, including the M4. My newer bike is a TREK 8000 with the ZR9000 frame.
I love it.
Great frame.
It has taken some really hard hits which gouged the paint off but underneath is baby smooth ZR9000.
I'd buy another one of the exact same material in a second and am actually considering buying a ZR9000 road bike frame.
Lighter than titanium, stronger than steel--what else do you need to know?