Sound quality for the Hesh 3 is a little better than the 2, particularly in the higher-frequency ranges. Their weight is noticeably less than their predecessor, and the cups are a much better size and shape; they fit much more comfortably around my ears for longer periods w/o any discomfort, and their rotating capability makes it easier to adjust them on my head as the day wears on. Bluetooth pairing is solid, and the battery lasts for a very long time. (I suspect, like the Hesh 2, the battery will last longer than advertised).
These headphones absolutely great. I am not at all disappointed and highly recommend them to anyone who's looking for an awesome pair of headphones for a very reasonable price.
I *do* kind'f wish it came with a carrying bag like the Hesh 2 did, but this is a minor concern.