For reference I updated from a Series 0 to a Series 4 with a cellular plan.

  • To get the bad out of the way first, my only real disappointment is Raise to talk to Siri. Sometimes it works like magic but 50% of the time it doesn't activate. It makes me feel awkward and self conscious when I talk to my watch and absolutely nothing happens. I have not figure out why. OK, the rest is positives...
    • Well, there is one other thing that really bothers me though I knew about it ahead of time: The Watch should be able to stream music to my car's Bluetooth. Inability to do this is a major chink in the "ok to leave your phone at home" concept.
    </li>
  • Size: I went from the 42mm to the 44mm and was a bit worried about the size since my wrist is on a bit small. But the 4mm looks ok on me and feels smaller and lighter than the old 42mm.
  • Appearance: When the iPhone X came out I didn't plan to do an upgrade. But while having a battery replaced at an Apple Store I gave it a look and a feel (!) and instantly wanted to upgrade. The Series 4 doesn't have the same impact but it definitely looks better than the Series 0 and has something of the look of the iPhone X.
  • Display: Really bright, very clear, and functionally seems much larger than the physical increase would indicate. I turned text size down to the smallest setting.
  • Water: I like to listen to music when I shower and it was always annoying to be in there when songs came on I wasn't in the mood to listen to. I wear the Series 4 whenever I shower and I can use both touch and voice to control my music. This is pure joy for me.
  • Infographs: I am using both of the Infograph faces. I have a Modular face set up for weekends and the other set up for weekdays because I have a different focus on those days. I welcome the addition of these new faces but I like symmetry and some of the complications around the edge have one design (e.g. arced with a color gradient) and others have a clashing design (circular). It took me quite awhile to come up with complications for each corner that didn't feel off balance. I'm only using 2 of the sub-dial slots (top and bottom, left and right are empty). Aside: for some reason the AQI complication often fails to display any data even though the UV complication always works.
  • Sleep: I now sleep with my watch on. Partly because I am using AutoSleep to track my sleep pattern and quality and partly because I hate having to unlock my watch when I first wake up. It's great to be able to give Siri commands via my watch as soon as I get up (my iPhone sleeps in my office, not my bedroom). And AutoSleep works well.
  • Battery: I've had the watch a couple of weeks and I have never gotten it charged to 100% since I'm sleeping with the watch on. I usually charge the watch a couple of hours in the evening and with that the battery hasn't dropped below 18%.
  • Performance: It's great. Don't know what else to say about it.
  • Wallet: My Series 0 wasn't responsive enough to ever use the wallet/Apple Pay. I would always feel like a nerd when I tried and then it would fail in a shop full of people. The Series 4 works perfectly so I use the Wallet several times a week.
  • Connectivity: With all the options in Series 4 with cellular it has naturally been quite good. But it's only a 4/5 stars so far. Normally it will operate just fine if my iPhone is far away within the house or I leave it at home. But occasionally the watch seems to spend quite a bit of time figuring out it can't talk to the iPhone and needs to switch to WiFi or cellular as appropriate. The delay can be on the order of 10 seconds which is more than enough to be highly annoying. I'd rather it err on being more aggressive in connecting on it's own.
  • Health: Sometimes it would take me more than a minute on my Series 0 watch to start a workout. It was incredibly frustrating to have it lock up while trying to do so. Naturally it works perfectly now. The heart info feeds into AutoSleep and my workouts but I have no known heart issues so I can't speak to the other features. Also, I haven't fallen...
  • CARROT: I'm a long time fan of the app and on the Series 4 it is a delight. I paid for the upgrade so I can use it's complications on my watch faces.
  • 1Password: I sync a few credit cards, library card and my drivers' license info. Essentially this is "I forgot my wallet" mode.
  • Radarscope: Because it's cool to have a weather radar on your wrist! It works well on a Series 4.
  • Apps: I do have 24 apps installed but other than those noted above nothing else is particularly remarkable (e.g. Yelp, Hilton).