If it could replace the need to carry a phone around with me, or have one clipped to my belt, or have a bag to carry it in, etc. It's far nicer to have nothing extra to carry, than to carry around an item.
It would need a replaceable power source that holds a long enough charge so years from now when the battery doesn't have full capacity, it lasts all day and into the night.
It would be nice to have a scalable sized display, perhaps projected if not holographic (there goes that power).
Google Now functionality required, so connectivity, location awareness and microphone please.
Instead of being a watch, be the band, so whatever watch face could be used. Come in a size/style that suits womens watches.
It doesn't need to have a speaker, that could be a separate Bluetooth earring like IBM had 15 years ago, so the entire world doesn't hear/be disturbed, and I don't look like a borg.
One of those virtual keyboard systems that can tell what your fingers are typing in midair from your wrist movements. Acceptable to have a complementary bluetooth bracelet for the other wrist to make this work.
In the future, I'd like a private neural display, so I'd be a 'borg, with an amazing firewall so I don't get mental adverts. At this point we'd hopefully be able to eliminate the secondary bracelet for typing and just think "OK Google".