https://arstechnica.com/gadgets/2018/09/apple-watch-series-4-review-a-bigger-better-watchos-experience/

The fourth iteration of the Apple Watch still looks like a tiny iPhone on your wrist, but for many, it was the most exciting device announced at Apple's event earlier this month. A  larger screen, faster performance with improved sensors, fall detection, and ECG readings are just a few of the features that inspired quick interest in the Apple Watch Series 4. The steps forward in health monitoring alone point to a new era for Apple's wearable, and users who could benefit most from them have a compelling reason to shell out $399 or more for the Series 4.

Otherwise, the Series 4 is an amalgamation of small improvements that make a big difference in the Apple Watch experience. These improvements will attract new users to the Watch who have been waiting for a device that's up to their personal standards, and they will make existing Watch wearers question their happiness with the smartwatch currently on their wrists. But while the Series 4 represents the first major redesign of the Apple Watch since its birth, that alone doesn't make it an automatic upgrade for all Apple Watch users.