I really liked my 5 Pro. But the Ultra, in my opinion, is a big step forward. Mainly, the battery life. I've seen reviews that dis the battery. But in my experience so far, the Ultra's battery goes twice as long before I have to charge it.
I also like the square styling of the Ultra, as well as the new band attachment mechanism.
My only complaint is the band itself It's too short for my wrist and I had to buy an off-brand one. Even the OEM 5 Pro band worked on my wrist, so I don't know why the Ultra's band is shorter. But that's okay. I prefer metal bands anyway. I sent the OEM band back for a points credit.
The watch is absolutely fantastic and really durable, the battery lasts a decent enough time as well. The only issue that I have is the band seems to have really negative effects to my skin.