The Fitbit has, from I can tell, the best hardware when compared to other watches and "Superwatches", but there software leaves something to be desired when compared to competitors like Garmin Vivoactive, Basis Peak, Pebble Time and the new Apple Sport Watch.
Improvements:
Notifications:
The first improvement that should be made is the intergration of other apps for notifications. Not many people use messages as their main form of texting anymore and leaving this out limits Fitbit compared to other brands. Adding notificaations support can be achieved as it is with all of the competeitors. Use the https://developer.apple.com/library/ios/documentation/CoreBluetooth/Reference/AppleNotificationCente...
Although it should also be noted that there are some notifications you don't want to recieve on your watch which is why a switch should be made in the app to say which apps are allowed, something like this. 
Stronger Alarm:
The second improvement has to do with the alarm. I think it should be stronger or at least repeat itself untill stopped. Usually the vibrations do no wake me up forcing me to return to a tradtional alarm instead.
New Features: (Endless Opportunities)
SDK - Clock Faces:
A new feature that should be introduced is the watch faces customisation. Competitors allow the watch face to be created and be customised, for exmaple pebble and Garmin. The watch face should be personalised and allow people to get what they want on the watch screen. For example the seconds and the date on the Flare clock face. Allow a community to be created where people can share their clock faces with eachother, similar to other brands.
SDK - Apps:
The other feature is the introduction of apps. This is a major part of the new fitness trackers and smartwatches, with things like Garmin's ConnectIQ and Pebble Time's app. Allow people to create third party apps for the Surge and make it a proper competitor in today's market. Open a community of developers to Fitbit and make it a competiative brand. It is endless what things could be done if the watch could be used with a simple app like a compass or stopwatch like these.


(The stopwatch wouldn't include the GPS or the distant)
Or could go to something complex as with Garmin, Apple and Pebble's apps.
Links of Ideas:
https://www.reddit.com/r/fitbit/comments/2uf6ql/hackjailbreakroot_fitbit_charge/
https://community.fitbit.com/t5/Feature-Requests/3rd-Party-apps-that-can-be-developed-by-anyone/idi-...
https://developer.getpebble.com/
https://developer.getpebble.com/smartstraps/
http://www.wareable.com/apps/the-best-apps-for-pebble-and-pebble-steel
http://help.getpebble.com/customer/portal/articles/1701779-pebble-appstore
https://apps.garmin.com/en-US/
Moderator Edit: Added Labels/Title for Clarity
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