I've owned a BMW, a Lexus, a Corvette, two Subaru's, and two prior Mercedes. The Bluetec gets the ribbon. It has a tight, solid, heavy and luxurious feel, but the torquey motor gives it plenty of punch. I feel safe in this car, even at high speed. It has air bags everywhere, and the TeleAid system (similar to OnStar). It has a tight turning radius and is no problem to park. Visibility all around is excellent. And it is not ostentatious to the point that vandals want to mess with it. The automatic tranny does have the annoying and well-known habit of "hunting" between 1st and 2nd briefly when starting out, but I've learned to ignore it! My friend's Audi had the same problem. No biggie to me.
The fuel economy is great. Around Seattle (very hilly, lots of stop and go) I get 25MPG. On a recent trip to Phoenix the computer was reading 41.3 MPG on flat highways at about 60 MPH. At highway speeds a 700 mile tank of gas is no problem. Also, the car's service interval is 1 year!
The NAV system (NavStar) stinks, and will have you driving in circles. The upgrade DVD is $280. Buy an aftermarked Garmin! Also, if you live in a hilly region like Seattle, Sirius cuts in and out so badly it's not worth the hassle either. Finally, it would be nice if MB offered AddBlue for the '07.