I have a love/hate relationship with my Ultra. I love it, because it is Apple. I hate it, because it is lacking compared to even a basic Garmin.
I wear it 24/7 unless I'm charging. I run/swim/cycle in it. I've done races and triathlons in it.
The battery life has gotten worse over time. In battery health it still shows 99%, but my charging has become more frequent. Still, I love that I don't have to worry about charging my watch every single day any more.
I'm hoping the Workouts app improves. A lot is lacking for running. I've tried a refurbished $99 Garmin Forerunner 245 recently and it was a lot better. My coach gives me exercises every day and it is a pain to enter them from the Apple Watch. Garmin can just sync. I'd settle for even just being able to enter them in from my phone. There needs to be some way of managing your previous workouts. Sometimes I have a ton show up, and then sometimes only a few to pick from. It is so hit or miss that I have started to enter them in and naming them by date and no longer reusing previous ones - again a pain to do from the watch. I know it is trying to be smart and guess what run I might want to do, but I really just need a way of organizing them, deleting, and having a clear way to get to a previous one I want to reuse. I want to be able to enter in my actual heart rate zones instead of ones the watch estimates. I want to customize the screens. I want to customize the screen when one part of a custom workout finishes - this one is extremely frustrating. I really want to be able to adjust how hard it taps me on the wrist - the Garmin was very strong and you won't miss it, but the Apple Watch Ultra gives a wimpy tap and I've missed it countless times when I'm next to a busy street.
Siri - poor Siri. It never works right. It is more frustrating than just pulling out my phone or fiddling with my watch.
Probably not Ultra specific, but I have my Shokz headphones connected by bluetooth to both my phone and watch. Sometimes I leave my phone behind, and just want to use my watch. In this case it all works great. If I bring my phone with me, I end up having music playing from both my watch and phone way too often. This should be handled a lot smoother. This might also be a Siri issue.
Weight/size - I'm used to it, but I wouldn't complain if they made it less tall and weigh less.
I'll probably keep wearing it, because I do like the look of it, I like how it is tied into Apple Music and it is just good enough to get by as a fitness watch. It is disappointing to be talking about their flagship model as just good enough though. I get it that probably most people that buy it are just using it as a fashion accessory, but I feel like they could really improve a lot of the software to make everyone happier.