As Suunto's endurance community manager, I've gotten the Ultra, Sport Wrist HR and now the 9. I really didn't expect it to be a better experience than the Ultra, but it has been.
It has a newer GPS chip, so it performs better there. I really appreciate the "hours remaining" indicator in the activity pre-start screen. One day, I got in the pool with very little battery left; I think less than 5%. At some point mid-swim, I noticed the screen was off so I figured I'd miss tracking most of the workout. I don't know the full specs on this, but apparently it kept tracking because once I got it plugged in, the activity was still rolling and it hadn't missed any yardage from my entire workout. Very impressed with that.
The subtle design changes vs the Ultra and the Sport series are excellent (sharper bezel edge; exposed, uncolored metal on bezel top and between bezel and body; sharper, longer buttons); subtle, yet excellent. And while the band is barely different, it just feels better. All I can say it try it on after wearing an Ultra or a Sport for awhile and you'll just know that it is.
Of course, there are still some software hiccups (Movescount mobile app + Suunto mobile app; set pool distance to meters and the activity display shows Yards if you're on imperial; likewise will show meters if on Metric and you set pool distance to yards) that need cleaning up, but those will come as much has improved on a steady basis since the original Spartan launch.
If you pair with other devices, it's been flawless with my Rotor 2INpower and Stryd Summit. I turn on 24/7 HR to monitoring myself throughout the day and mostly while sleeping. I don't exercise with HR (power & perceived effort on bike and run; pace and perceived effort in pool). I'm primarily training for road triathlon, though I use it to track treadmill, indoor/stationary bike, SUP, alpine skiing, hiking, trail running, mountain biking, yoga/stretching and others. I customize all my regularly in-use sport modes. I did that via Movescount.com on desktop. I know it's an option now with the Suunto app but I haven't needed to make any adjustments since that came out. I have used navigation of routes multiple times and love the feature. I don't think it's a loss at all that the watch doesn't store maps or music ... more storage and hardware power for better accuracy. And honestly, if I need a map I will pack a paper map with all the details or download Google Maps for offline use so that I have bigger perspective to work with.
Excited to see what's next.