The 'new shape' Panda is actually now over 10 years old in its design (introduced in 2012). The primary thing over the previous model is it is bigger in every direction. This means more space, better ride and safer (a lot of the added size was because its stronger, the doors are thicker and so on). On the other hand, it's also a bit heavier. When introduced it did well in the crash tests of the time. It still would, but the scoring system has changed and using the latest version of the test it got no stars at all! It's not less safe than it was in 2012, just the goalposts have moved. Much of what it 'failed' on in more recent testing is a lack of modern safety electronics like collision avoidance or 'stay in lane' systems, or 'only' having four airbags. It's still a lot safer than a 169 model.
The old Panda was very similar to the 500 (and made in the same factory). Apart from the engines and, apparently the heater unit, practically every other part is different post-2012, notably the suspension system (the car is a fair bit wider now). There's more 'elbow room' in the front and more legroom in the back. The boot's bigger too. It needs a little more space to park in though.
More recent versions of the Panda (but also other makes too) have had engine tweaks to give better environmental performance – the Euro 6 standard – but these come at the cost of less enjoyable on-the-road performance. This seems to be particularly true of the 1.2 petrol engine. The 'engine of year' winning TwinAir was hailed as a marvel when introduced, and in lab tests had unbelievable economy and low emissions. Trouble is, they were just that: unbelievable in the real world. So poor in fact that Fiat dropped that engine from most of its models in about 2018 because in the newer 'real world' tests it was way off the mark. Same for the diesel (MultiJet), which was much worse with NOx emissions than earlier lab tests suggested. Still a good engine though - mines a 2018 diesel! It still has lower carbon emissions than the petrols and easily averages 55mpg in my 4x4.
Summary: compared to the 169 model its a huge leap forwards. But, compared to newer designed cars lit is now definitely not as up to date especially with tech and safety stuff. I love mine though ... and Im on my third 312 model.