I test drove the Fiat 500 and it was fun to drive, but I felt these were its big drawbacks:
1. Safety. It gets a 3 star rating, whereas the iQ gets 5 stars. That's a dealbreaker for me - especially in a microcar. In general, there's no way I'd buy a car that got less than a 4 star rating.
2. Roominess. My 6' 3" boyfriend told me he would never be comfortable in it, and I don't blame him.
3. Gas mileage. It gets approximately 10 mpg less than the iQ.
4. Reliability. Things may have changed, but historically the Fiat has been so unreliable that Europeans joke about it.
5. Design. I generally love a retro-modern look - when it's done right. My home decor is a mix of modern and retro. But I'm not sure Fiat got the mix right. I don't love it's design, and I feel like I'm someone who would love it if the designers had really hit the mark. I don't think it's god awful, like the PT Loser, but it's not quite right. It's like I really want to like it, and I keep trying to like it whenever I see it, but it never captures me.