I have been in the iPhone world for about 5 years. Always wanted to try Android, I have nothing against it since I'm really not an Apple fanboy. Going to the Nexus line was a logical move for me, I like the simplicity of the pure OS that works exactly how it's maker intended it.
Talking about the 5X I have absolutely no problem with the plastic build, the screen is ok, the camera is good, wifi speed is fine, great FP reader, etc. I don't play games, I use my phone for email, Viber/Whatsapp, reading webpages, occasional Google maps, so I would define my usage as moderate.
BUT:
Maybe I am the unlucky one since I have experienced almost ALL of the issues that others are complaining about online. In the first few days the phone got so hot around the FP area that was uncomfortable to keep in my pocket, not to mention putting it on my ear to talk... it was crazy. First night it lost 40% of it's battery sitting on my nightstand. All stock apps, just what I mentioned above (and no FB). I've gone to developer options and selected "no background processes", with no success it seems. Only a factory reset made the device stop heating. A week later... again, the same thing.
I need a battery app, a cache cleaning one and constant monitoring during the day to make sure that I don't find it losing half it's power by sitting in my pocket. The quick menu lags and freezes every few days, heavy webpages are a nightmare to navigate. The camera app has lag that bad that I miss shots on a regular basis. Why? Why should I have to do all those things, and why these apps, written by the same company who created the OS are unable to do their job well? It's nice to have the option to install third party apps if you want to, but it's crazy that YOU HAVE TO in order to be able to use your phone.
If this is the showcase of what Android is about it's a big disappointment. I know that the 5X is not a flagship, but nevertheless it should be able to do what was designed to do. They say it lags because of the encryption. Fine, but why include encryption on hardware that is unable to handle it well? Coming from the iOS world it seems CRAZY that I even have to consider disabling services like location, 4G or WiFi, essentially crippling the phone just to be able to get through a day.
With the usage mentioned above the best I got was 5.5h of screen time which I consider to be very good, but usually it's just 1,5-3h and the thing that bothers me the most is the inconsistency. If it last 2h... fine, but today it's 1,5h tomorrow it could be 4 or 1, who knows. It's unreliable and that's why I'll switch to... I don't know, I'm thinking about the 6P to give Android one more try. No way am I paying for that horrid TouchWiz UI.
iOS has it's drawbacks for sure, the locked system, the 7 years old home screen, I REALLY hate that I can't customize the notifications that I get on the lock screen, but if I trade optimization for customization I am not expecting to also get inconsistency and unreliability. If a phone has 5 functions it should be able to do all of them well, otherwise, what's the point?