I like how the airspeed indicator freezes and shows a reduced speed when flying for too long inside a cloud
Also there are really usefull shadows! I was trying some multiplayer flying a 109. When zooming down from the sun to surprise a lost spit i notised not only my shadow on the ground infront of me, but a second shadow! Looked behind me and sure enough there was a spit on my tail which i managed to get away from