BMW and Mercedes switch places periodically in technical and design leadership, and I think it's Mercedes's time. BMW has been going off the rails recently...
The prototype design looks much more sleek to me, but I'm not a car guy, and I think all modern cars are ugly.
There's a lot of visual conflict between the two motifs, as shapes that normally have boxy, sculptural depth get squashed down into basically 2D features on the surface of the smoothed out, mouse-like volume of the overall package.
The designers seem to have been stuck with the assignment of putting a Mercedes mask onto a wide, flattened jellybean. The result is mostly successful from the side views, but seems pinched and overwrought from the front.
Additionally, some of the grille shapes on the front are likely vestigal, as EVs don't require the same ventilated cooling as combustion engines. Much to the frustration of car designers, one of the key identifying features of any brand has historically been the design of the now obsolete front grille; the functional purpose that served as an aesthetic starting point is now gone. (You can trace the gradual acceptence of grille obsolescence in the evolution of Tesla's designs.)
I was all excited about replacing my 2007 Prius with the new one, but now I'm not so sure. Perhaps I'll wait for the Lightyear 2 which is hugely more slippery at a Cd of 0.175.
There was never a reason, aerodynamic or not, to make the design look so ridiculous except if you’re the GM of the 3 Series or S class you don’t want someone else eating into your sales with a different product line.