I fucking love the scene of Gandalf removing his grey robe, and how he's kind of got this subtle glow to him. I feel like it's a much more effective portrayal of magical power than some dude flinging fireballs and lightning bolts, just having a guy literally glow with power.
The soundtrack for that scene's also amazing, the choral parts are some of my favorite bits in the LOTR soundtrack
My favorite part of this is the sound effects Gandalf's magic makes. As soon as you can see his staff, you can hear rolling thunder in the background to really emphasize what's happening - take that away and it's just an old guy saying corny lines.