Here are some observations/impressions from a lazy-bugger! Granted the Fenix paired with an Android phone will do most of this (and many of these are not unique to the Apple Watch Ultra, so regular Apple Watch users would have this), but these are just the things I've noticed over that last week or so.
Comfortable on wrist with both the ocean band and alpine loop. Alpine loop probably wins for comfort but more finicky to put on. Have a trail loop on order, will let you know what that one is like
Easy to operate. Touch screen is intuitive and pretty responsive. Only found it tricky when trying to swipe left/right or up/down to switch between screens, while moving (running... if you can call what I do "running")
Occasionally a button gets bumped or the little one touches the watch face and apps get opened etc. I believe there is a way to have a "lock screen" but I think one sacrifices ease of use (or has to deal with the hassle of unlocking) if they opt for this
Easy to manage settings and watch faces through Watch app on phone. Almost no need to ever go into settings on watch
Battery life - This being a big point of contention as I know one can use the Garmin if they are stranded in the amazon for weeks, whereas the Apple is pretty much a "charge daily" device. My daily use has been: put on in the morning. Standard use all day, including about 1hr of workout time with GPS and GSM doing their thing. When I go to bed the battery is typically at about 75%. I could still wear it for sleep tracking, but as I don't like wearing a watch to bed, I just put it on charge. It charges in less than 1hr and a notification pops up on my phone telling me when it's charged. This works for me. May not work for those doing multi-day back-country adventures, or those that want to wear the watch 24/7 with minimal downtime.
Seamless iOS pairing. Like seriously seamless. It just works
Connectivity - my mobile provider here in Hobit-land allows me to add a GSM enabled smart watch to my unlimited mobile plan for a fee (7NZD or about R80pm). This means I can go out for a cycle/walk/run without the bulk or risk of a phone in my pocket and can still send/receive calls, texts, whatsapps and emails. Now most people leave phones behind for a reason so don't care about this. BUT another useful thing with the GSM connectivity is that I don't have to pre-download Spotify playlists. I can just stream the music while I'm out and about. The downside... this drains battery life faster. The upside, when the watch is in range of the phone again, the mobile data mode goes into standby.
Apps - any apps my iPhone had that an Apple Watch version were automatically installed at setup. Any I didn't want were easy to remove through the Watch App on the phone. Haven't installed any watch specific apps yet, but I'm pretty sure one could get almost anything they want. The downside... most have some sort of paywall for all the features
Automation - For those who have used Apple Shortcuts on their iPhone, this is old news... but for those that don't know, this is a very basic "logic builder" to automate certain actions based on a set of criteria (basically if-then). This couples with the Action Button on the watch (which can be used to run Shortcuts) can be very powerful. For example, one can create a shortcut that takes proximity to a specific location (ie. the gym) into account, and presents an appropriate action menu for that location. So if the current location is close proximity to the gym then the shortcuts in the menu will be the Start Workout for whatever activity one does at the gym (treadmill, squash, weights etc), but if the current location is close proximity to one's home then the menu can adjust to be control of smart home devices (door locks, lights, speakers etc). Another useful one could be to send an automatic "I'm in a meeting" reply to an incoming call/message by simply pressing the action button (no need to pull phone out and look rude), and by taking one's calendar into account. It can take some time to build these Shortcuts although it's not too complicated and there are websites (like https://shortcutsgallery.com/) where one can download premade sets of logic. Overall can be pretty darn powerful if one puts in the time to build some good ones.
I'm pretty simplistic in this regard, due to my non-competitive nature coupled with my laziness 😅
Activity Rings - I already had on my phone but paid no attention to it. With the watch it's more useful and I find it pretty cool. It's where daily goals for Standing (1min/hr), Exercise (minutes where heart rate exceeds a brisk walk) and calories burnt are all tracked. Steps are also tracked and play into this, and if one dives in there are some pretty interesting stats available, like step asymmetry (% stride difference between each leg) or "sturdiness" are analysed and tracked. I think much of this is actually done by one's phone being in their pocket. Again. probably nothing new for Android or Garmin, but my novice observation thought this was cool, and better than the simple step count my old Fenix 3 did.
Heart Rate - Plenty of YouTube reviews on the accuracy, and generally it's supposed to be pretty good. The ECG function and detection of anomalies is a plus, although shrouded in plenty of disclaimers, classic Apple style. ECG's can be exported to PDF too to be shared with a medical professional
Workouts - The app is pretty intuitive and does most of what I need. Some workout types are fairly generic, like Outdoor Cycle, which doesn't differentiate between MTB, road, etc. It seems pretty smart too as I was on a walk the other day with some friends. I forgot to start an "Outdoor Walk" activity, but after about 10min the watch took my elevated heart rate and movement into account and popped up with a suggestion asking if I was on an outdoor walk and if I wanted to track it. I confirmed and it back-tracked most of the previous 10min activity to add it to the workout, I thought that was pretty slick
I haven't looked into it but there are plenty of 3rd party apps for the more serious athlete out there
Whilst these are subjective (and I have openly admitted to preferring the rugged look of the Garmins), I have found that with watch face and aftermarket straps, the watch can transform for most occasions.
I know the Garmins have face and strap customisation options too, but the retina always-on display from the Ultra is pretty sharp, so many apps with custom designed faces, and so many strap options available for dirt cheap (from places like Amazon or Aliexpress), plus the straps are super simple to change. It's like having more than one watch.
I have created a bunch of custom watch faces, similar in appearance (simple and clean) but themed based on function, which I can easily flick through after tapping on the current face (no need to delve into the settings or use the phone app). For example:
Here's what they look like IRL with an aftermarket black alpine loop (from Amazon)
And here's another with an aftermarket titanium bracelet (also from Amazon)
Anyway, those are just some initial impressions and observations based on my limited knowledge. Again, I know most other smart watches can probably do most of these things, but this may be helpful for those looking at the Apple.
*Garmin Flame Suit On* 😅