However, the W210 and W211's were mostly known as quality disasters. The W211 fixed its problems toward the middle/end of its run, but it will go down as a sub-par quality Benz. The later W211's and especially the W212 which has launched more or less flawlessly for a luxury car, is what brought M-B so far back up the quality charts (as a continuation of course of the W221 and W204's before it which were the "return of the old-era, new era".
I used to think M-B's were masters at facelifts, but not so much these days. The W204's face is a slight downgrade I think, especially with those terrible reflector lights, and the GLK facelift made ugly even uglier, IMO. They just started on this whole "redesign the car for the facelift" kick, which is uncharacteristic for them, and IMO not working well.... not for those who bought a previous model and expects M-B timelessness and confidence in product design, nor for some of the new extensive facelifts (hits and misses, but for those hits, I say "why not from the get-go? I.e the W204 interior. Why not design it appropriately right away? It looks like M-B admits fault, and has to correct themselves.... not a good look at all).
Of course, style isn't ONLY what sells the cars, but considering the W212 on paper looked a lot like the W211, and was probably the most aesthetically hyped and controversial Mid-Size Luxury Sedan since the E60, I think it's the styling that has made is such a huge sales hit namely in the U.S, where it has sold extravagantly. As a buyer in this class, the E might be the most "iffy" from the beginning, but it's so much more of a characteristic and distinct demeanor from the very homogenized Mid-Size Sedan lineups we have around.
As for quality, no arguments there, I'm sure the quality will only get better with the F.L, which is great as the W212 is of top of class quality already (statistics behind that one).