The Concierge said:

I've never really understood the reasoning that Obi-wan and Yoda ought to appear as idealized projections like Hayden-Anakin did. There are obvious crispy and darkish factors affecting Anakin that don't apply to the others.

It would seem established that once you become one with the Force and gain the ability to appear as an apparition, it is restricted as you appeared when you died. Not a problem for Yoda and Obi-wan! They have all their limbs! So either way, unless you want a horrifying vision of a reanimated, disarticulated corpse bidding Luke farewell (which would follow established "canon", and morbidly make the most sense...), there HAS to be an idealized, kind of wish-fulfillment ghost-projection of Anakin.

But which makes the most sense? A vision of what Anakin *could* have been, but never actually was? A kind of mystical plastic surgery? Is this perhaps more vain than the Force should be? Or do you go the route of a vision of what Anakin *has* been, the Force reaching back to the "good man who was destroyed" (debatable though it may be exactly how "good" he really was)? Or is that still the Force appealing to Anakin's vanity?

Personally, I prefer the idea of going back to a younger version of himself. But it's not a slam dunk case by any stretch.

If you wanted to take the idea that the force ghost looks like the person when they died to be literal, then we would have to acknowledge that Ben should have appeared beheaded. The only interpretation that is consistent within the OOT only, is that the ghost appears as remembered or idolized by the viewer.