Plus, as the icing on the cake: you can easily get a week or more of use with a single charge, if you don't use the GPS.
Automatic sleep tracking is abysmal (regularly off by >4 hours, sometimes more). The wrist heart rate monitor tends to have inaccurate spikes at least once a day, and when the watch doesn't detect motion the wrist heart rate sensor is essentially turned off (sampling rate goes to greater than once every 30 minutes). Resting heart rate is calculated in at least 3 different ways in various parts of the UI (and none of them seem accurate). And then there's the tons and tons of bugs (and terrible iOS companion app).
Honestly the hardware is ok, but I get the impression that Garmin just hasn't invested in (or doesn't know how to do) software. It's not worth the (very high) asking price in my opinion.
It works almost flawlessly. GPS pickup is less than 30 seconds in nearly all situations. The wrist-based HR is accurate to within 1-2 BPM during activities when measured against Wahoo Tickr and Polar heart-rate straps (but the flaw: it's slow to pick up sudden jumps in HR, such as during intervals). The battery lasts at least a week with 2 hours of active GPS use a day (and almost 2 weeks with battery saving features enabled and GLONASS off). I've dropped it on asphalt, concrete, and rock and it doesn't even have a scratch.
My guess is that most of your problems are on the iOS end. Apple is notorious for breaking interoperability with wearables through iOS "updates" since the iWatch was released. Polar and Suunto watches also seem to have issues for iPhone users that don't crop up for people syncing their watches with their computers or Androids.
Garmins are buggy though, but once you get used to working around the most common bugs they are quite reliable.
I think Garmin just had the best devices in the early days, and now rely more upon brand loyalty (myself included) than technical advances. Touch bezels in the Forerunner range deserve a special place in design hell though.
(Granted I'm not the average Garmin user as I'm more interested in ultra-distance.)