Basically nothing so far. Though there were minor issues when the car was brand new:
Engine light used to turn on - that caused a loss of power and jerky ride. Dealer remapped the ECU - it sorted out the problem.
The hood was not aligned correctly - the gaps between the hood and the headlights were seriously uneven. That caused some efforts to close the hood. Dealer fixed that.
There was a lack of coolant (about 1 litre) in the system - dealer filled it up, but I had to pay for that extra coolant!..
Recently I've noticed that a handbrake has some too much free play, and there's some squeaking sound coming from the engine when idling. I think dealer will sort that out at the first service.
All in all, no big problems, but quite some issues, which were overlooked by the manufacturer.
This Fiesta is for someone who wants a small vehicle and economical ride. Basically, it fills those needs quite well. The plus sides would be:
Nice seating position. The steering column is adjustable in 4ways - so almost everyone could get a nice fit in the driver's seat.
Good visibility - large windows and lifted seating position sort that pretty well. This Fiesta has some traits of a small minivan - the body and seats are higher than those of previous generations. By the way - this trend is seen in many small hatches today.
Comfortable ride. It's really smooth and absorbing for such a small car. Also the seats are quite comfortable too, offering a good lateral support.
Smooth engine. It's tuned to have all the power and torque at low rpms, so it's easy to ride in everyday traffic. The best grunt is between 2000-3000rpms, though even below 2000 it drives well (if not loaded up), and it's useless to rev it past 3500.
The looks. This is of course personal preference, but I think the styling inside out is one of the strongest points the Fiesta has.
It's quite roomy, even at the back (keeping in mind that we are talking about class B hatch), and has a full size spare tire.
Handles well. The steering is responsive, weight well balanced, the ESP works well if you get yourself in trouble. The weight of the clutch, the power of the brakes and steering - everything is well matched.
Now some downsides:
Not that economical. Ford claims 3.7 highway, 4.7 city and 4.2 avg. In reality you need at least 5L/100kms average. Of course, if you'll drive steady at 80kmh (50mph) you will get 3.7L/100kms, and if your city is without traffic and traffic lights, you might get 4.7L/100kms. But as I prefer some extra speed, my average consumption is a little more than 5 L.
The driver's seat could adjust lower. At its lowest setting it's quite high (I'm 5'10 if you're wondering).
There's no coolant temperature gauge. I find that a bit uncomfortable.
The trunk lacks an extra compartment (or just a stretch net) for small items. And in my opinion the trunk could be some 5cm shorter, allowing more leg room for rear passengers. It's a small car anyway; if you have a big load, you'll need to get the rear seats down anyhow.
In conclusion it's a nice car. Fills all the basic needs of moving around. Feels like a real car too, not like some small shaky bucket with a motorcycle engine.