I have the Series 2 and it's been great for me.
1) Vibrating alarm. Perfect as I hate these big vibrating discs for the deaf. They break frequently.
2) Message/Email notification. It vibrates when I get a text message so I can look and see if it's worth my time to reply or wait till later. Same with email.
3) Fitness - great for running and can even leave the phone at home (Strava especially).