Here is my breakdown of a month of using the Nikon Z6 mirrorless full-frame camera.
+ Faster autofocus performance
+ Better performance in low light and higher ISOs
+ Fantastic video performance with 4K/30fps, even with DX lenses
+ In-body stabilisation helped me nail shots with lower shutter speeds without blur
+ Fantastic lenses available for the system, the S line in particular are amazing (even the entry level kit lenses)
- Only takes one XQD/CFExpressB card, they aren't cheap
- Not the best for continuous shooting compared to more expensive cameras
- DX mode only yields 10MP pictures so not ideal for crop photos
- Most Z lenses are quite expensive with a few exceptions