Help me out...what's the big difference between those movies. ..? I watched esb to rotj at least 200 times and still don't see it. .. and now rots. ..
The main difference is with the helmet. In the original movies it was hand-sculpted and asymmetrical and painted in an alternating black and silver (so it would stand out better on film), and that's what gave him a lot of his menace and personality. In ROTS they made the mask smaller, perfectly symmetrical, and all black.
Vader was also a lot bigger and beefier in the original movies while in ROTS he was played by Hayden Christensen who was of course a lot more slender. There are lots of other minor differences, but I'd say those are the main ones.