I really like what you've done with this figure. My one suggestion is that when doing black - especially a glossy reflective black like on Vader's helmet - I find it helpful to leave some areas of straight black, and a few spots of gleaming white. The transitions in those spots should be extreme, unlike what you'd see on fabric or something matte or semi-gloss. When doing star wars guys in particular, given their odd propensity for wearing riding boots to all occasions, I find it's useful to grab a pair of my wife's show boots, turn a lamp on them, and see how the light plays. If I don't do that, I end up talking myself out of painting them the way they'd look because it feels bizarre to apply the colors that way.
Your painting on this guy has inspired me to bump my unpainted Knight Models Darth Vader up to the top of my to-paint list.
Remarkable work. This miniature is really underrated. I love the OSL lightsabre and the smooth black. It is a real pain in the ass to paint the whole model with a single color but you pulled it off convincingly. The base is outstanding, too.