Just walked into the Yas Mall store, (Abu Dhabi) mid-morning. Surprisingly they had what I wanted in stock, and including the slightly feeble queue outside, the whole thing took about an hour. (Online it was showing 4-5 weeks for delivery). I got the 44 mm silver seashell sports band version. I have small wrists, but it is fine. It is light, comfortable, and feels quite a lot thinner than my old one, partly due to its larger height and width. I am very impressed with it. It feels and looks significantly better than my Series 2, and I much prefer the strap to the plastic one. Well worth the upgrade in my opinion, not least for the cellular connectivity. The face can display so much more info, and everything I use it for 95 % of the time is accessible via the complications, so I will hardly ever need to access things from the app screen, which I have always found somewhat tedious to use.
UPDATE: The screen is a significant increase in size. It actually makes a huge difference. The speaker is also much better. If you are wondering if it is worth upgrading (from any model) I think this is a very significant improvement. I am not a blind Apple fan boy by any means, but I am very impressed indeed with this watch. If in doubt, go for it!