I'm seeing a lot of these posts here. I think people are missing the point.
The 3-Series is a "core model", it needs to look timeless, it needs to age well. The CLA is a trendy design chalk full of fads that probably will age poorly, therefore putting a strong date-stamp on the design. This is kind of its intent, as it will provide it a lot of immediate fashionable hype, which as hype usually does, will wear off, while the 3-Series will more-so look fresh in a decade from now.
My personal opinion of the CLA are awful proportions due to a stubby FWD chassis, and erratically superflous lines which make no sense, a cartoonishly featured face and a droopy behind.
That all said, this car is not in a 3-Series' league, and once people see and drive it in person, they will most certainly realize that. This is a FWD Econo car, make no mistake, with what will be a terrible use of interior space. It won't have any engines larger than a 4-Cylinder. This won't be as sophisticated nor mature a car as the 3-Series (or C-Class), it won't be as "prestigious" if you had to pick one in that element. This car is aiming for those who like the design characteristics of a car like a Lancer Evo, but don't want a Mitsubishi. This car is about being brash and immature, and it has an inherently Economy-Car like substance to make it feasible to its intended market.
I think that any success of the CLA IF it can still sell people on the historical "prestige" of the Mercedes brand, although it's a FWD car starting under $30K, would force the C-Class and its 3-Series rival to move up in public perception.