Some of the updates from the 620 that I like are a bigger crisper screen, a longer battery life (from 10 hrs. to 16 hrs. in GPS mode), text/call alerts, activity tracker, sleep monitor and a few upgrades to the use with the heart rate monitor, downloadable screens and widgets from Garmin app.
All of these updates also include the functions that already exist in the watch from the prior version , built in pedometer (if running indoor or don't feel like waiting for a GPS singal), color screen, touch screen, and cycling mode.
The activity tracker is pretty cool because it includes my run for the day, so it is nice not having to switch between different watches. The watch will also ibrate after a period of no activity,
The increased bttery life is a noticeable and conveinet. I only really charge the watch once a week.
The smart notifications are cool. The two most notable apps are weather and text/call alerts. It's cool to look at a text real quick on your wrist without having to take out your phone and the weather app is nice for the same reason.
Overall it's a great watch, Im sure it's even more impressive when using a heart rate monitor but I don't usually wear one. I have not used the cycling feature yet. I would imagine it's not too different that the preavious model.