Background: Pebble user since the original Kickstarter, had several of those. I've been using Garmin products for ages for running and cycling. Briefly flirted with the original Samsung Gear band (what a POS that was). Went to a Garmin Fenix 3 HR when they got iOS notifications, thus combining high-quality fitness watch with sorta-smartwatch. In short, I'm sold on smartwatches, and do endurance sports.

Objectives: notifications so the phone can stay in bag/pocket. The more "phone stays in pocket" features, the better. Must function as a standalone fitness device (IOW, must have GPS; syncing later is an expected compromise).

Series 4 is finally the perfect storm to get me to buy one. The first ones had no GPS or water resistance. I'm not paying that much if I still have to keep a Garmin around. Series 3 added LTE. Ah, now I can go for a long run in the woods and leave my phone at home. But I'd laid out big bucks for a Fenix 3, and meh, nothing about the 3 really grabbed me, and by then I was used to ignoring the Apple Watch. But with the 4, it looks like Apple decided to make the fitness aspects stop sucking. IOW, maybe I could use this as a running watch, too. As a person who has Wolfe-Parkinson (heart condition fixed with ablation), the ECG piqued my interest. Now, doc said I'm fixed, so ECG shouldn't be an important feature. But it got me thinking, which led to talking to the wife, which led to "well, why don't you just buy one, then?".

"Well, maybe I just will."

"Buy me one, too. Silver aluminum with nylon band."

"Yes, dear."

We've not had them but a week, but I'm more impressed than I expected to be. (I mean, I'm really impressed, but I don't want to drip fanboi on anyone, so I'll tone it down.) The stock workout app would do just fine for most folks. If you're not most folks, WorkOutdoors has been impressive the few times I've used it, and there's RunKeeper and the like. We used the LTE functionality first day we ran with them to co-ordinate (we run separately, with dogs). The screen, OMG, it's head-and-shoulders better than my Fenix. Raise-to-wake is reliably better than the Garmin (you'll need raise-to-turn-on-backlight for the Garmin in anything but outdoor sunlight or a bright room). It's gettin' dark here in the PNW, and for my old eyes the Apple OLED is easier to read on a dark run than the Garmin backlight reflective.

As far as the "smartwatch" part, I'll just summarize and say that IMO it's the best smartwatch going right now. YMMV, or maybe that's not even all that important. Of the functionality the Garmin replicates, the Apple version is just much more refined. As one example, if there's a notification on the Garmin, better hurry and look before it goes away. Apple waits until you raise your wrist to look at it before the timer starts.

The Garmin will stick around in the rotation. Even as a close-to-three-hours marathon runner, I wouldn't trust the Apple battery to go the distance, let alone anything longer. If I'm knocking around on wooded trails, the Garmin will probably take a hit better than the exposed glass on an Apple. IOW, serious outdoor work. But I'm not as adventurous as I used to be, so for everyday-carry I'm really enjoying Apple's offering.