With the Series 3 and watchOS 4, Apple continued to push the Apple Watch steadily forward in 2017, above all making the important leap of adding LTE cellular.
The upgrade meant that people willing to pay the premium for a cellular model — branded with a special red dot — were suddenly able to make phone calls, send text messages, talk to Siri and more while leaving their iPhone at home. Apple did make a gentle push in that direction with 2016's Series 2, which added GPS for some offline tracking, but with the Series 3, people were finally able to stay in touch outside of Bluetooth or Wi-Fi range.
The Watch still has some ways to go before it achieves total independence. An iPhone remains mandatory for setup, updates, and installing apps, and some functions may not be available over cellular. A Watch also has to be associated with an iPhone number, and you can't roam internationally.
U.S. carriers have been a little draconian in their data plans, too. Typically it costs an extra $10 per month to use a Watch on LTE, even with a generous iPhone plan. Exact subscriber numbers are unknown, but the online world has seen plenty of backlash at the idea of spending $120 per year on a smartwatch.
With or without LTE, the Watch became a little more practical in 2017. For fitness fans watchOS 4 added new coaching and challenges, and an improved Workout app with upgrades like high-intensity interval training (HIIT), better swim tracking, and GymKit sync with compatible cardio machines.
It's hard to tell where Apple is headed going into 2018. There have been hints of the Watch getting an EKG monitor, but little else has been rumored about a "Series 4" or "watchOS 5," except maybe the addition of native podcast support. Apple will presumably keep pushing in the direction of making the Watch independent — though it's hard to see the company completely detaching it from the iPhone experience.