First things first:
1. A week with the Watch is far too short a time to really evaluate it. These are going to be, inevitably, barely more than first impressions.
2. The WWDC keynote announcement of WatchOS 2 meant that we all know what Apple really wants the Watch to be, in its first full year of life. It seems pointless to criticise the first version for not having features that are in developers' hands right now. I'll try to limit myself to a discussion of what's already here, but keep in mind that some missing stuff is right around the corner.
Battery Life
People worried about this when Apple didn't mention it at the launch, but it's just fine. In fact it's great. As I write, at 22:35 at night, my Watch is showing 50% remaining power—and I've used it plenty since 7am this morning . As I said a few days in, we'd benefit more at this point from faster charging on the Watch than from a longer battery life. That will change of course, as future OS features use more power, and as future hardware sensors need to do more, for longer. The ginormous (2m) charging cable which comes as standard has stayed plugged in in my bedroom since I've had it, and feels plenty secure when magnetised to the Watch. It rotates to any position relative to the Watch, which makes me think there's a rotating element inside, though I haven't studied the teardowns properly. Certainly you don't need it to be in a specific orientation to charge, so you can snake the cable out any side you like. It sounds like a little thing, but it's surprisingly convenient. I'll buy a 1m extra cable sometime for convenience when travelling, and I normally have a couple of chargers with me (though I might take my double USB output iPad charger with me on longer trips abroad).
The Watch
I adore the Space Black Stainless Steel Apple Watch, and haven't regretted ponying up for this model for a second. I love the extra weight over the Apple Watch Sport, much of which comes from the link bracelet. Before the Watch arrived I was expecting to want a leather band or the Sports band to lighten it up on occasion, but I haven't really felt the need to swap the band so far (though I'd love a Product Red band for days when I don't mind being noticed).
It was a tiny bit fiddly to swap out the links since the release buttons are necessarily tiny and flush with the strap, but that's not something I expect to do often. My slim wrists meant dropping 6 links, which are stored in a neat soft pouch that comes in the box. I wonder if you'll be able to get spares under AppleCare, should you need them? I haven't removed the band itself yet, though when I tried it at an early in-store demo it seemed very easy to do. When I get an extra band I'll let you know.
It's kind of strange evaluating such a tiny device as the Apple Watch body itself from a hardware perspective. Apple's made plenty of small devices before (some, like the buttonless third-generation iPod shuffle, significantly smaller than this one) and it's no stranger to attention to detail. This feels like a different order of product though, something with so much functionality, so much integrity, and so personal, yet subject to so much attention.
It's not hard to see why people have approached the Watch as if it were a tiny iPhone, or indeed a tiny Mac. It has all the requisite components of a standalone platform device: Screen, custom input devices, audio I/O, wireless communications, a battery—even a (hidden) data interface. The degree of integration is remarkable though, even for Apple, and in practice all the parts merge into one, as if it were an object summoned out of metal and glass by some unknown process akin to magic or alchemy. It's much more like jewellery than it is like a piece of consumer electronics. I love wearing it, and yet I can't quite explain why.
The Watch Experience
While the Watch clearly is a tiny computer, it just feels wrong to talk about hardware and software separately. What Apple's aiming for here is a seamless experience, more like an iPod than a Mac, or even than iPhone. This of course is complicated by the Watch's (for now, and already decreasing) reliance on a paired iPhone, but it's a clearly signalled intention. At its best, the experience of wearing a Watch feels like wearing a discrete accessory (in the jewellery/fashion sense) that just happens to know about iCloud.
There are, inevitably, rough edges. Some reviewers have complained that the relationship between the functions or modes of the Watch is hard to discern. Certainly there's some complexity in the variety of ways one can interact with the device—the Watch faces, customisations and Complications; Notifications, both static and those offering user feedback buttons; Glances, which offer a single-screen view onto an installed application; and Applications themselves, which currently exist as a kind of projection from within a connected iPhone app, but are due to get a brain transplant in WatchOS 2 where the application logic can run locally on the Watch.
Of all these ways that one can interact with it, applications are probably the least interesting—for now. You'll spend most of your time looking at the Watch face, and interacting with Notifications. One exception for me has been the Messages app, which is a pretty slick way of responding to a message. I've answered dozens of messages on the Watch since I've been wearing it. Occasionally Siri has let me down, and I've reluctantly had to pull out my iPhone (as an aside, everyone's saying how good Siri is getting, and they're not wrong).
What else? I've had a few problems getting raise-to-talk Siri to actually act on instructions, though it does fine when I press the crown. It can be a bit slow setting timers with Siri, unlike on the iPhone. I initially set my activity levels too high, and the Watch dialled it down for me (I'm expecting it to dial it back up next week, since I'm filling the rings easily now). Having Lark on my wrist to nag me to walk around is pretty neat, and Lifesum's gorgeous notifications are definitely getting me to drink more water. Paying at Starbucks with Passbook feels like the future (roll on Apple Pay in the UK), and The Trainline's Watch app showing a graphical representation of soon-to-arrive trains is lovely. I've answered a quick call on my wrist, but rejected many more (very handy).
I'm hesitant to even try to provide any kind of definitive judgement on the Watch, after only a week. Nevertheless, I'm convinced this is going to get even more interesting, and that Apple takes this space very seriously. I'd been initially hesitant about climbing on board with the first model, but I'm glad I did. I'll have much more to say about the possibilities as the next few months unfold, and as I begin to work with designers on the potential of Watch-based applications, particularly in the area of healthcare. More on that soon.