1 - The
Mavic 2 Pro has the much larger 1in sensor whereas the
Mavic 2 Zoom and the original Mavic Pro use a smaller 1/2.3in sensor similar to what's used in mobile phones. The main benefit of the 1in sensor to me is the wider dynamic range but you need to process the raw files to get that advantage and if you're using the pictures automatically straight from the drone you won't see the benefit. I've seen a reasonable number of users here who are disappointed they paid more for the
M2P and were not seeing the benefits. The
Mavic 2 Zoom's camera advantage is more straightforward in that you get a 2x optical zoom
2 - The
Mavic 2 series have obstacle avoidance sensors all round although personally I avoid doing anything risky with the drone, the sensors are far from foolproof
3 - The
Mavic 2 series bodies are identical and it's only the camera/gimbal parts that are different, there's no compatibility with any of the parts with the original Mavic Pro.
I bought a Mavic Pro just after launch and then upgraded to a
Mavic 2 Pro shortly after its launch because I wanted the larger sensor. I mostly use full frame sensor cameras and found the small 1/2.3in sensor frustrating to work with on the original Mavic Pro since there's not much you can do with the raw files from it which is typical of a sensor that size. There are other small upgrades on the
Mavic 2 series which I appreciate but I wouldn't have upgraded for them on their own without the upgrade.