Screen angle and brightness I experienced the same on some Android devices: when changing the angle the screen is looked at, I see that the image gets darker or brighter.
I would like to know if it is so on all devices or just some of them.
This is affected by the manufacturer of your device, as well as your own device settings. Different manufacturers use different types of screens for different devices. Some of the different types are: TFT-LCD screens, as well as different kinds of AMOLEDs. I have had one Sony and one Samsung, and have noticed that even though the Sony has higher pixel density and brightness, it cannot be viewed from certain tilts and when natural sun light reflects on the screen, its content goes practically invisible until shaded.