My Parents have had a 500 TwinAir Lounge from new, for the last 3 years & 32,000 miles. It's been a damn good car. A couple of minor bits replaced recently before the warranty expired (anti-roll bar bushes and washer pump), but other than that and a random flat battery at a year old, which never occurred again, it's been fine. It's fun to drive, reasonably economical (46-50mpg pretty consistently), still looks good & (on the Lounge at least) has a decent level of equipment.
Other cars have tried and failed (so far) to replicate the 500s sales success - the Renault Twingo and Seat Mii/Skoda Citigo get decent reviews, but I've seen 2 new Twingo's on the road, and no more than 10 each of the Seat & Skoda - I've probably seen a hundred 14 plate or newer 500s in the same time frame, so the 500 obviously does something well for many buyers.
What lets it down, and what has meant the Parents are not getting another Fiat, are the constant price increases and the poor customer service. They need a 5dr car, so another 500 was out of the question, but they could've still got a Panda, 500L or 500X. Trouble is, even a Panda 4x4 is as much to buy as a bigger Nissan Juke, and if you look at the Juke's closer rival, the 500X, you're looking at about £2000 more to get the equivalent model Fiat.
If you spend that premium, you expect solid backup if something goes wrong, but the way the family's been treated by Fiat HQ over problems with my Sister's Alfa MiTo is very much like Fiat just can't be bothered. It's 'unfortunate' that problems occur, but that's what the warranty is for, and people should be grateful for that. I'm afraid with the prices they charge, Fiat Group can't expect people to settle for this nonchalant attitude. As such, the Parents are buying a Nissan Juke. Not my cup of tea to look at, at all, but it was refined, with a strong engine, a dealership that looked like it'd actually had a bit of money spent on it, and things like 3 years servicing for £199 - one service on the 500 was £370!
Whether Nissan GB are any better than Fiat UK remains to be seen, but when you're saving over £2000 on list price versus the equivalent Fiat, it's a gamble worth taking. We know the Fiat will be at least as good a car as the Nissan, but chances are the backup will be average to appalling, so why spend a premium for it?