I share your same considerations. After the theft of the Silmarils and the end of the Noon of Valinor, Morgoth is indeed supposed to manifest himself in Arda in his usual terrible appearance, as he had done during the previous wars against the Valar (Years of the Trees) and long before. I would nonetheless say that, at an extent, we can notice some different aspects from Annatar: that is, Morgoth's face already shows the corruption of his essence and the scar inflicted by Thorondor.
There's also another motive that interests me. His expression doesn't express malice nor evil intentions, but rather a sort of subdued feeling (sadness, in a sense, with the broadest connotation): the tragic condition of being evil and not having the possibility to redeem in any way, as if he were a slave of his own character.