Well I'm no dentist.. In fact my teeth are pretty, well, rubbish.
f/2.8 lens: Total Non-Big deal. Even at night, no mirror= almost zero vibration, coupled with the in body image stabilization.
Fixed lens: How many people have never even taken a 35mm lens off of their Leica M?
No (built in) Viewfinder: Sure, it'd be nice but the height of the camera would no doubt suffer for one.
With practise I'm sure that with a Brightline finder one could quickly become adept at guessing where the mark was and using the spot AF. I use a brightline finder anyway (on an M) so it's another total non-issue for me.
Gimme!
I would agree that it's on the pricey side, but it's Leica, and no doubt given time the price will come down. For the same money I would take one of these over an M8, almost no question.