I've only had my mix 2 for a few days. I've moved on from a 3 &1/2 year old OPO so it was easy to be impressed.
It's really thin. It should have been "fatter", to make the camera flush with the body and accommodate a bigger battery. It just feels so thin, even with the case on. Cameras have gotten a lot better since the last time I was in the market for a new phone, SoC's too, no lag or stuttering. Battery life seems great initially, I can only imagine what the original mix was like. Enough space in the chin bezel to incorporate capacitive buttons, maybe it will happen for the mix 3. The other 3 bezels are definitely there, the rounded corners aren't helping but I'm not bothered at all. Speaker is quite loud, not as shrill as I'm used to hearing from phone speakers.
Excellent fit & finish. It is a good phone, with minimal changes it could have been a great one. If Xiaomi makes it easier to buy their phones internationally, opens up stock android options and doesn't go mainstream but rather have the mainstream follow their bold mix 1 concept, they can skyrocket their market share. Especially with current pricing, they can go from "a alternative flagship" to "the flagship to buy".
MIUI is definitely quirky. There is a setting that's enabled by default, it won't let you use mobile data to download apps. Unlocking the bootloader is complicated. MIUI account is mandatory to gain "admin" privileges. Lots of bloatware, most of it in Chinese. The global or EU ROMS are needed. The phone is functional enough once play store and access to google apps is there but if you are used to nexus/near stock Android experience, you will want to tinker.
I have no issue with lack of waterproofing, never owned a ip rated phone. The ceramic won't survive a fall, even with the included case that has no "lip" protecting the screen.
I think I made the right decision already but custom, stock oriented ROM's will make it a lot better. If you want to make a stand against the rising prices of flagships, mix 2 and the original are a good place to start. From the US, the original can be imported for $405 and while it's camera, display and SoC are 2016 standards, it holds up well especially with value proposition in mind. The early adopter fee for the mix 2 is slowly fading, once it settles at $500, it'a great alternative to $700+ flagships.