For me, charm and character.

I was an original Pebble Kickstarter wearer from 2012, then got the initial Time, then the first Android smartwatches (Moto 360!) then basically every Apple Watch from then to now. Even used Google Glass a few months in 2013.

I like my wearables. I use features on my Apple Watch constantly: NFC payments, voice reminders, fitness and sleep tracking, make my iPhone yell out so I can find where I put it, etc.

But not a single damn wearable I've had has captured a fraction of the charm the original Pebble and Pebble Time had. Their UIs are low-res by modern standards, and greyscale or largely solid colors, but wow.

Dug up some videos as reference. Here's one that highlights what the core system UI aesthetic is like. Notice the transitions as you use the UI. I remember it feeling really snappy too, and it feels great to use a UI that moves like that with physical tactile buttons, as opposed to scrolling a Digital Crown or using the touch screen on an Apple Watch:

https://www.youtube.com/watch?v=SdRENEQcymQ

And aside from the system UI, the community of apps that existed for it back then and no doubt will continue to grow now has a lot of charm too. The creators of all the apps are making them out of love, not to be a Top 10 on an Apple app store. And they don't exactly have a strong cohesive system UI to comply with unlike Apple. Human Interface Guidelines are wonderful for phones and tablets and for serious app ecosystems I depend on, but watches are Not That Serious as far as I'm concerned so the individuality and love within each app just fills me heart with joy every time I look down at my wrist.