Has an always on display, apart from  that I dont see much different from a physical viewpoint.

Always-On Retina display. You no longer need to raise your wrist or touch the screen to see the time or other information on your watch face, because the display never sleeps. So whether riding a bike, cranking out some crunches, or counting the minutes in a meeting, all you need to do is glance to find the time or your workout metrics right there where you want them.To remain on all day with all-day battery life, hardware and software have to work in harmony.2 The display dims when your wrist is down, yet key features, like watch hands, remain visible at all times. Touching the face or raising your wrist brings everything back to full brilliance.

Apple to continue to sell series 3 but not 4, series 5 same prices as series 4 was. Entry level series 3 down to US$199!