There is no app drawer which mean the home screen will be more cluttered, and instead of using the regular Android design elements you can see influences from the iPhone around the OS. The Xiaomi MIUI9 model solves theses issues, however.
The 3210mah battery is large, and you'd be hard pressed to completely use it up in a day. The Snapdragon 615 chip which is used isn't the most efficient, and the screen takes up a good amount of power as well - the only things preventing this phone from having great battery life.
It even includes a quick charge feature (not Qualcomm's branded QuickCharge), which can deliver a 40% charge in an hour or a full charge in 3 hours.
The 5" 1080p display is very good for a phone that costs this little. The resolution is great, colors are vibrant and accurate, and viewing angles are great as well.
The Snapdragon 615 used is the second generation, improving performance over previous Snapdragon 615 processors. It scores 2656 in GeekBench 3 - a very respectable score, and handles just as well in games.
You can install a new theme on your phone through the built-in theme store, or download more themes. These change the color scheme in the system UI and icons.
In well lit scenarios, you'd be hard-pressed to find a better camera. The 13MP sensor has a dual tone flash as well as a f/2.0 aperture. In low light scenarios, it can introduce noise and over saturation, but results are still admirable considering the price. It is capable of recording 1080p video at 30fps, or 120fps slow-mo videos at 480p.
Most phones (even expensive, high end phones) only come with 32GB of storage, but the OnePlus 3T starts at 64GB with an option to go up to 128GB. This should be more than enough for most people, even after considering that it doesn't have a SD card slot.
The OnePlus 3T has a larger than average 3600mAh battery, which allows it to last the whole day every day. GSMArena gave it an endurance rating of 83h (1 hour of talk, 1 hour of video, 1 hour of web browsing, then idle until the battery dies), which is quite a bit better than most other phones.
Instead of the plastic clad phones of yesteryear, the OnePlus 3T is encased in a metal body this time around. While the design is remarkably similar to the HTC 10 (and HTC One M7 - M9), it feels solid and looks great.