The plug-in version of the tiny 500 turns out to be an all-around excellent car.
There are a couple of good points to having that heavy battery pack. First, since it's attached under the car, it keeps the center of gravity down low. In turns, the 500e doesn't wobble like a baby toy. Plus, that battery pack is bolted to the car's body, helping to stiffen it so that it resists twisting. Again, that makes for better handling and more fun.
Also, 600 pounds has a way of smoothing out the ride. Considering its size, the regular Fiat 500 doesn't take the bumps too badly to start with but the 500e it very nearly rides like a miniscule luxury car.