So far, I'm very happy with the upgrade from the Pro 2 to the Pro 3. As others have mentioned, the new eartips take some getting used to and caused me some discomfort, especially at first. Apple's own software, which tests the earbuds for a proper fit, repeatedly prompted me to put them in. Ultimately, the standard size M turned out to be fine. They also had some initial trouble pairing with my iPhone, and switching to a MacBook was very slow compared to the Pro 2. Although I think this was more of a software issue, because I haven't had any problems since.
Furthermore, the sound is much better; the bass is more prominent compared to the Pro 2 version. This is definitely a noticeable difference from the previous generation. The ANC has also improved slightly, although I have to say the step from Pro 1 to Pro 2 was much larger than from Pro 2 to Pro 3. I would recommend these earbuds everywhere, but if you have the Pro 2 version, an upgrade is certainly not a must. Think of it more as a refined version of the pro 2.