My Fenix is the middle-sized one, but when I got it that was the only one (47mm). Garmin released a smaller version (S) and more recently a larger version (X) that are mostly just cosmetically different (though the X tends to have a few features the S and regular do not share).
While mine is several generations old - exactly how many is less straightforward than you might think since Garmin can't count each generation with a new number - my observations apply to all the Fenix series watches. The watch is slate grey and it came with a black band. The metal ring (which acts as, or protects, the GPS antenna) is the part anodised slate grey. It scratches moderately easily. I first purchased a genuine Garmin green silicone band for a bit of colour, but the band broke very quickly. I then bought three off-brand silicone bands (green, blue and yellow) and despite their low price, they have outlasted the Garmin band by years.
I find the watch vibrates a lot during mountain biking. Enough that by the third day of lift-served descending, my wrist could have a hole in it where the watch rubs on the skin. Doing the band up a notch tighter does help, but it also can make it feel too tight. In fact, it vibrates enough that on several occasions the main button has been pushed causing the watch to stop recording. Reverting the watch to watch mode protects the recording function because the button would have to get pushed twice to achieve stop.
Someone I know recently purchased an X-sized Garmin. It is only 4mm wider, but it looks so much larger than the regular one. He told me that his new watch moves around on his wrist less than his old, regular-sized watch. That was enough of an endorsement to make me consider buying an X.

I always use the Fenix in dual mode - where it uses both GPS and Glonass satellites. On road this isn't so important. Off road this is much better for accuracy. It gives a small hit on the battery life but I seldom get close to running the watch down in use.
While I read lots of stories online about the Fenix series not holding power meters well, I have used mine with at least 2 different power meters without encountering any dropouts in connectivity.
I once had an issue where the watch froze. I sent it back to the dealer and they got in touch with Garmin (or sent the watch back to them, I'm not clear on this part). All it needed was for me to upload all the files in the watch to Garmin Connect and then delete the lot from the watch. It was just a memory issue. It hasn't recurred in the years since. Weird.

With the recent release of the Fenix 7, there was also an Epix 2. The Epix only comes in the middle size like I have now. The difference for the Epix is the OLED screen. It is considerably brighter and more colourful than the Fenix passive screen, it offers more pixel density - it just looks better. Unfortunately there is no Epix X (or I'd probably have one already).

In many ways the Fenix line function like an Edge bar-top computer for the wrist. That is good, because the Edge line are well done.
Even better, the Fenix is not in the "sporting" line of Garmin products, but in the "outdoor" line. No lives depend on the sporting, so the firmware is usually released before it is 100% right. The outdoor line is considered essential survival gear, so the firmware rarely goes wrong (either early in the lifecycle or at any subsequent point).
Both the beeping and the buzzing could be more attention grabbing during a ride - it is easy to miss them on the bike most of the time.

I reviewed a much less expensive Garmin when mine was very new. That model would identify sporting activities as they started and record them just in case you wanted to record that sport. The Fenix doesn't do that. I got to work and it suggested I had just been on a bike ride, would I like to save that activity? Pretty clever.

It is almost impossible to read the screen with the watch hand on the bars. If you really want to read it, it could go around the bars and point up towards rider's face. But that gets the heart rate module off the wrist where it can function. Yes, I usually use the HR chest strap for greater precision in HR, but putting the watch on the bars is a slow task and prevents any use of the HR module.

After 6 years of using the Fenix and 7 years of using my Edge bar-top GPS, both could probably use a refresh/update as the battery doesn't have the original run time any more. I am seriously considering foregoing a new wearable GPS and going with only a bar-mounted one. A lot of expense goes into squashing everything into a watch-sized device. The Fenix 7 I prefer is about 3x the price of the Edge 530 I also prefer.

There are some options that the Fenix gives that an Edge lacks. I run DH ski mode for lift-served cycling which gives me run-by-run data and a count of how many runs were done (and then in Strava I swap it back to cycling and it reinterprets the data in that light). I also use the Fenix for walking and the like - I could skip all that for a new Edge, but I might miss it. While the old Edge and old Fenix continue to function pretty well, I can keep thinking about my future needs.
Incidentally, I have had opportunity to use quite a few other GPS brands, from a Suunto watch to Wahoo, Bryton and Xplova bar-top units. Each has appealing aspects, from being less expensive to more customisable. I don't think I'll go away from Garmin any time soon.