Just updated a couple days ago. So far, so good. If you have other Windows 10 devices, the consistent experience across them is great. Groove, Cortana, apps, etc. Phone experience vs. 8.1: 1) Messaging is better, more polished, and I like replying from the banner notification without opening the message. 2) Calendar and Outlook Mail are significant upgrades. They just feel better and built for the enterprise, which I like. 3) Groove is light years ahead of 8.1 Xbox Music. 4) Cortana - been good, no complaints. Like everything else, having the same experience between my phone, work PC, and home laptop is great.
Only thing not as good as 8.1 is the battery but it's still decent. It's draining a bit more quickly but it's only been a couple days. Looks like I should be able to get around 24 hours with my usage when before I was closer to 30.