The Castellans of Dol Guldur are deadly spirit guards of the Hill of Dark Sorcery. A creation of GW, they fit well with the themes and flavors of Tolkien's works in my opinion. They are nameless and faceless spirits that have fallen to the control of the Nazgul in the past.
In the Strategy Battle Game they are expensive but deadly models, but I would rarely use more than one at a time in a 250-500 point army. In War of the Ring however, you need at least eight to make up a unit. Unfortunately GW only had two poses of these so a tray of eight would look pretty repetitive. Luckily the Morgul Knight models had a very similar theme to their armor and a few more poses available.
The flesh and gaps in the armor were painted pretty much the same as I did my LotR: Ghostly Legions...a base coat of gray, highlighted a couple layers to white, then given washes of green. To help with the glow-effect I allowed this to "spill out" onto the armor and cloths around and blended it in as I worked on those outer layers. The armor and cloths were finished with a rusted and tattered look and a final green wash was applied to the entire model.