I must say, this is a great form factor and we were really hoping more brands would get in on this approach. There are just times where you don't want the weight or expense/risk of lugging around a mirrorless camera. This camera is so small, light, and capable it's great for vlogging or documentary video as long as you can live with the wide focal length. But the 2X zoom on this 4 version is much better and appears useable.
This camera can literally fit in your pocket and feel like nothing. Now, it is more fragile than an action camera, but with a little care and effort you can work around that. And DJI's audio offerings are good enough and also small and light.
This camera as DLOG whereas the three had DLOG-M, which is the light version of DLOG and not as good (but better than no log).
If you own the 3 you can skip this generation and wait for the 5, but it still doesn't take away from the fact the 4 is a great, great portable camera with a good image.