If you read my Xiaomi Mi 4 Review, you'll know that the hardware and the software completely blew me away. It's easily the best phone you can buy right now, with some caveats. The main thing being that the power savings are way too aggressive, and third party system apps get killed. So things like new clocks, or two-factor authentication apps, won't work or won't be there when you need them. Even Google Music gets killed in the background silently. It's like using iOS all over again. Which is a damn shame because the OS is very very smooth and fast, and fun to use. So I've installed a Xiaomi provided Lollipop Rom (that gets regularly updated too!). Man, they did a great job. My only complaint so far is that their superior camera software isn't installed. They are apparently working on adding it.
And it's not that Google Camera is "bad", it's just not nearly as good as Xiaomi's. It's slower, and pictures aren't quite as good. Still very good, but not Xiaomi good. Battery life already appears to be taking more of a hit, but that's to be expected since background apps aren't being indiscriminately killed anymore. The main thing is everything works, and works very well.
I'm going to be doing extended testing over the next few weeks. If I don't find something that pisses me off, then the phone is exactly what it feels like to use. The perfect Nexus phone. Like a stainless steel and wood Nexus 5 with better.... everything.
Look for my update in a few weeks.