The car is larger with 3.7 inches of length added versus the previous model as well as a 2.0 inch longer wheelbase. This allows legroom to increase for the rear seat passengers by almost an inch. BMW claims the increase in size will not add weight with the F30 supposedly weighing 80 pounds less than the E90. That is something we will have to see when the curb weight tests come around for the new car.
The motor will be familiar except for the 328i which gets the new N20 4 cylinder. The 335 has the same N55 single turbo direct injected 6 cylinder. A hybrid model is also available. Overall, BMW played it extremely conservative with the new 3 and the good news is E90's will not look dated. Average people will likely have trouble even noticing the new changes.