if you really want to know:
1) Style (which is obviously a matter of opinion but lots of people like the style)
2) Build quality (better seams/materials)
3) Battery Life (Seems a lot better than all but the Pebble)
4) Tighter control of watch notifications (rather than funneling everything to the watch you choose which notifications can go through to the watch).
5) Glances, where are short lived application status screens you can see quickly.
6) Taptic feedback, which can be really nice over buzzing or sound and can tap you on a "side" of the watch apparently.
Those are the main points I can think of now. I think the main uses of the watch for most people will resolve around glances, I think a lot of people are getting watch apps all wrong by thinking the actual app will be opened much at all. Also if a watch app "pollutes" my set of Glances with a useless screen, I'll probably end up deleting the whole app from the phone.