The background colours give off a cosmic totality from Eru.
The esoteric quality of the illustration makes it highly compelling. Putting the Eruhini within Eru and under the Flame Imperishable gives it a touch of genesis, a beautiful creationesque quality.
The characterization of the Ainur adds magnificence to the piece. Detailing the regalia of the Ainur with features of their own domain helps mark them in such an elegant fashion. It is a mark of vision of a true artist.
What I would have liked to see is a representation of the void. I might be mistaken and it might be in there woven brilliantly and subtly -like everything else- as the void is an essential part of The Silmarillion.
Nonetheless, no words I can write can give justice to this masterpiece. I would say by far your finest work, but your other features of work are brilliant.
At request, please continue to illustrate such brilliant settings.