I'm still new to the D5200. I don't have a D3200 to compare. If you place the camera in Manual Mode and activate Live View you can change shutter speed and see changes real time. You can change ISO and see changes as well. You can not change Aperture, without exiting live view. You must exit LV, make Aperture changes and activate LV again. It's hard to see any changes in Aperture or Shutter Priority modes, because the camera compensate the other setting automatically.
Another way of explaining this: When I use manual mode, I have to set the camera to manual movie settings in order for the screen to reflect changes. If not I can change ISO and shutter speed to my heart's content but the display doesn't change.
Some comments from other forums:
"On Nikon prosumer cameras, with Shutter Priority in Live View video mode, the camera cannot automatically adjust exposure by controlling the lens aperture. Once you enter Live View mode, the lens iris can no longer be adjusted due to the mechanical construction of the mirror box."
"The Canon lifts its mirror to provide live view. To shoot a picture, it opens and closes a shutter curtain. This makes very little noise and allows the camera to quickly return to live view. The Nikon lifts its mirror to provide live view. To shoot a picture, it drops the mirror, opens it to expose the sensor, then drops the mirror again. (In other words, it uses the mirror
as the shutter.)"
Nikon D5200 Hands-on Review - YouTube