Styles aside, the Falster 3's hardware is pretty much the same as the Fossil Gen 5 smartwatch. It uses the Snapdragon Wear 3100 chipset and offers more RAM and storage than the second-gen Falster. There's also a new speaker and the case is now water-resistant up to 30 meters (or about 98 feet) so you can wear it while swimming.
Fossil also added its proprietary battery-saving modes to the Falster 3, which allow you to launch quick profiles like "Time-Only," "Daily" or "Extended Mode" and squeeze more juice out of the watch. You can finetune exactly what sensors you'd like to disable, like GPS, NFC and WiFi, to get more runtime. This feature launched on the Gen 5, and is not to be confused with the battery-stretching modes that Google and Qualcomm announced when they partnered to launch the Wear 3100. That hasn't been activated on many Wear OS devices yet.
The Falster 3 does also feature the Tiles interface that Google announced in May, and while it's not new and did already show up on the Gen 5 Fossil, it's a difference from the Falster 2 that I appreciate. The Tiles make it easier to get to widgets like Weather and Agenda, making Wear OS a little more similar to Samsung's Tizen.