Just me, Deeter26_2.
My turn for a cut at first impressions. I'm currently field testing the F5S (Black Sapphire) and it's pretty amazing.
I'm a F3 guy through and through but this new toy is equally impressive. There are several subtle improvements that capture my attention.
From the manual I noticed that it would be able to Lap While Paused. I've seen several requests for this ability although I've never seen the need or understood when it might be useful. Nonetheless, it's there and will be appreciated by some.
Also in the manual I noticed it has a GPS signal strength data field. Here's how it looks.

OK, maybe not exactly what folks have been asking for but again, I've never really seen the need. Accuracy has never been an issue or concern for me. The F3 has been straight up exceptional so no surprise that the F5S performs as well right out of the box. I suppose I should add that as a solid advocate of the GPS performance of the F3 I'm usually dismissed as a quack or someone who doesn't understand GPS quality or bends the GPS limitations to my own liking so that I can defend the F3. That's funny. I'm extremely demanding of GPS expectations especially when doing pace based workouts. I'm fortunate to be able to do workouts on a course with QTR mile markings by a certified race director. The F3 hits markers within 1-3 steps consistently. Never misses. On the one sample I have with the F5S it was equally remarkable. I get tired of defending the F3 since it's been so solid for me. For reference I've got about 5000 miles and counting with that guy and never been disappointed. With that out of the way......
Power Save alerts. YAY!!! Finally. Have wanted this on the F3 since the beginning so super excited to see it implemented here. OK, not the biggest of deals and I've learned how to not get bit when using the F3 but it's a simple feature on every Garmin watch so I really appreciate it on the F5S.
Auto Lap overrides laps in workout/interval mode. Not for me. Many people like this functionality but I'm in the other camp. It's super easy to create a Workout profile with Manual Lapping only (which I've done) so no harm no foul. The F3 flirted with this in beta for awhile but had some issues so never made it to production. Yay! Anyway, most new releases follow this method so I wasn't really surprised that the F5S has this too.
Metric Auto Scroll in paused mode. Super nice! I think this also comes from the Forerunner family. I'm not legally blind but I'm visually challenged. Severely. Like I can't read a thing on my watch without reading glasses and so out in the field I struggle. On pause, the F3 contains activity metrics that are invisible to me. The F5S scrolls the data in a large font that I can almost read. Nice!

Last Sport/Last Run widgets. Always wanted the F3 to accumulate weekly Run widget mileage regardless on whether I used Run, Trail Run, or Indoor Run. It was all running to me. F5S does this. Last Sport will give me stats for the last activity I performed. Last Run will give me a weekly tally of all Run subcategories. F3 will not. It treats Last Sport and Last Run identically and won't give me a snapshot of true weekly mileage. This is awesome! Although I actually prefer the widget layout of the F3

The shrunken 'hour' field. Noticed during a long run that my timer seemed to be corrupted or I had toggled to another screen or who knows what. Remembered that I had read somewhere that the hour field shrank, so quickly got orientated and adjusted. It just caught me off guard at first. The F3 does this as well so shouldn't have surprised me. It's just with my poor vision I completely lost the leading hour field. Probably just because it is so close to the outer edge that I missed it. Clearly the minute/second fonts are wider than the F3 and more readable. Anyone with moderate eyesight probably wouldn't even blink at this behavior.

Gyroscope. I'm only guessing but I feel like it might be helping in the area of distance accrual when I'm out in the trails. I spend a lot of time on single track wooded trails and have been recording slightly longer distance. That's cool! Like when I upload to a service that will recalculate based on recorded GPS points I come in almost spot on. The F3 accrues shorter. Again, I really don't fret about that. As a trail runner I get out to enjoy the terrain and let myself go. I'm NOT doing pace based training in that environment and I'm out there for the pure thrill of it. Anyway, point for the F5S here.
Battery Life. On a 3:45 run I went from 100% down to 66%. That gets me 11-12 hours in GPS mode. The F3 dropped to 74% so seems to be in range. I'm probably not running longer than 10 hours most days. HA!
Size. Did I say that I was an F3 guy? I'm used to it. I like the weight and bulk of it. The F5S just seems too small for me even though the screen size is the same. I know that makes me odd. MOST people will appreciate the build and beauty of the F5S cause it is certainly all of that. It's gorgeous. I love the Quick Fit straps. Wearing the F5S makes me covet the Chronos even more I think. I want big. I want bulky. The F3 is dreamy!
Enough from me today. I'll add more as I accumulate more data or discover new features. I wanted to add in some track data but unfortunately, MYGPSFILES doesn't support the new fit structure yet. Drat!!
Regardless.......this watch is a solid home run and I would recommend in a heartbeat!