I've enjoyed my M for the last month or so. Great call quality, solid battery, and I've yet to experience any kind of crash.
On the negative side, I'm not too impressed with the camera and I'm just not a fan of pentile screens. They're just not as sharp if you like to do a lot of reading on your phone.
I might wait to see if the M HD becomes a reality. The 4.3" screen loses some real estate to the on-screen keys, so the 4.5 would be a nice improvement.