Because it just works, has an awesome feel, notifies me, calls work, has all the apps I could ever need, is faster than ever, and is a slick design.
What more could I want. All the information I could ever need is available by just looking at my main screen - weather, numbers of emails/texts, date (even the calender icon changes with the day!), wifi status, network status, battery status - all with just a quick glance.