I am most often behind the wheel of 4x4 vehicles. I'm not married to that arrangement, but that's just how things work out between employment and weekend activities (you are NOT going to take the Fiat 500 down the ol' access road or abandoned logging road).
I do drive regular cars, here and there, and have pretty strong opinions about what a car should do: handle very well; go quickly; use relatively little fuel; not be a money pit; not look like a sculptural interpretation of the color Beige; carry four passengers and/OR have impressive track times. The Fiat 500 does most of these.
The engine is fine for urban driving and will pull you along the highways. I have not taken this model on a proper road trip and have no idea how it would react to mountain passes. I do not like the sound of the engine when it is tasked -- like a lawnmower. I wouldn't suggest that this equates to durability issues, but to my ears it does sound sloppy and unrefined.
Despite the clunky engine feel, the Fiat 500 is still fun to rev-up and zip through and around bothersome traffic.
Handling is great. This IS a city car and it does the city well. Cornering is very good and requires little braking compared to compacts like the Corolla or Civic.
The interior is odd, like an upmarket fast-food joint. Not really my thing, but I have seen much worse. Seats and dash scuff-up easily, but you can just buff 'em out.
Seating and storage are somewhat limited. However, I hope that no one would purchase this as a family car, and not doing so would leave a lot of storage with the rear seats down -- plenty for groceries or the typical owner's trip to Ikea or whatever. Not sure that I would make adults sit in back for longer than 10 minutes. Comfort is just average, though the seat backs are nice and tall.
Fuel efficiency is good, though my mind is not blown given the car's low size and weight. Around 33 MPG in town.
Live in a good-sized city? Hate trying to work your way around awful urban planning and traffic jams? This thing might do the job.
I do not understand the whole (USA only) tiny-car-as-fashion-statement trend, and find it and the participants annoying. In the end, though, I think that the Fiat 500 transcends this stupidity by being good at what it's made for.