I've still got one of the square sixth-generation iPod nano devices in my drawer at home, along with an expanding metal bracelet that turned it into a watch all the way back in 2011. To tell the truth it was never a good watch, and in some of the ways that people now accuse the Apple Watch of failing in its primary timekeeping function.
For starters, the display wasn't always on, although unlike the actual Watch you couldn't just raise your wrist or tap the screen to wake it and see the time. Worse still, once it was on even a brush of the screen would take you out of the clock functionality and back to one of the iPod's other menus. To be fair, it wasn't really meant to be a clock full-time.
The resolution and clarity of the iPod screen also left a lot to be desired, and meant squinting at it in anything approaching direct sunlight. Apple Watch isn't perfect (where by 'perfect' I mean as readable as an analogue watch in bright light), but when I wake in the night it's a whole lot better than the Casio Waveceptor I was still wearing a few weeks ago. The Casio's luminous dial needed a few hours of stored sunlight to work correctly (it was never going to get that stuck up my sleeve in the UK) and always faded before my eyes could adjust.
The nano's battery rarely lasted me a full day of listening to stored podcasts (with the earbud cable snaked up the inside of my sleeve) and checking the time, though it saved some of my iPhone's battery for other things. I'd always have to take it off and charge it when I got home from work, and I rarely wanted to keep it on when I wasn't using it for music. The Watch is so comfortable I want to wear it all day, and thankfully the battery keeps up.
I'm reminded however that the nano came with a lot more watch faces than Apple Watch currently has—sixteen in total—including colour-matched ones (the nano came in seven colours) and no fewer than four from the Disney/Henson stable (Mickey, Minnie, Kermit and Animal). Some of the regular watch faces were pretty crappy, but I'd have those Muppets on my Apple Watch in a heartbeat.
(Postscript: Just reminded of Geoffrey Goetz's piece at Gigaom, which usefully outlined all the things that Apple needed to fix if they actually made a thing for the wrist)