(It would be long. I'm sorry ^^ My inner philologist is hard to leash)
I think, what appeals to me most is the fact Eol's the only one (well, as far as I can remember from Silmarillion) who, being able of pretty dark deeds, has no Doom, nor Curse, nor Oath to corrupt him in the first place (and doesn't give a damn about Silmarils). With Professor's words that every story is a story of the Fall (plus Mortality and the Machine), Eol really puzzles me, as he hadn't any particular Fall, he is just the way he is from the beginning. Yep, "dark", I think, is a good word ) And he never pretends to seem otherwise.
While of Maeglin I used to think, like, "oh right, here goes another one" -- noble looks, crafty words, the type who makes everybody (well, almost) like them and then lead them into some nasty kinslaying (like it was with Feanor, CCC and Turin, it feels like one of Professor's favourite combinations). It was so very strange and kind of eye-opening to discover fandom's different interpretations. It's so great your depictions of Maeglin (on the wall too) are much deeper and far more compassionate than my old headcanon, I'd probably never be able to see there's so much more in him. I'd love to see a drawing of him around the Fall of Gondolin if you'll ever come up with one : ) It woud be interesting to compare it with his father's image and that child with hopeless eyes.
Aaaaand I wonder what's your take on Eol :3