I have yet to fully test the OnePlus 5T's camera and whether the extra four megapixels make a real difference, but the camera seems great from the few pictures I've taken with the phone so far.
Like the OnePlus 5, the OnePlus 5T has a portrait mode for the rear camera, which I still need to test. If the portrait mode from the OnePlus 5 is anything to go by, it should work quite well on the 5T. Unfortunately, it's still lacking a portrait mode for the front-facing 16-megapixel selfie camera, which would have been a good update for the 5T to include, especially as the Pixel 2 phones and the iPhone X have selfie portrait modes.
The secondary camera lens also appears to be designed purely for the portrait mode, and there's no optical zooming like there was on the OnePlus 5, or the iPhone 8 Plus, iPhone X, or Samsung Galaxy Note 8. That means the OnePlus 5T zooms digitally, which generally isn't as good as optical zooming. OnePlus says the zoom results should be just as good, but it's a claim I'll have to fully test.