It's interesting to note that some versions of Ultimate Ultron in the art book depicts him as having his mouth and eye areas glowing the same way as he does in the comics. The more I think about it, the more I wish they just went and made Ultimate Ultron's face straight-up based on his traditional comic visage.
I think it would have made sense in terms of how Ultron was essentially deprived of the final form he had wanted for himself. Ultron clearly designed his Ultron Prime form to be more humanoid, with his intended final form being practically a full-on android (Vision's body). When his plans were compromised, he obviously had to take a more literal approach in terms of upgrading his Prime form (applying vibranium coating), and I feel that reverting it to the classic visage would have communicated that desperation on his part as it gives off a really robust vibe to the design like the Mark I, in stark contrast to the majestic form of Ultron Prime.
I think it would have made the confrontation between Vision and Ultron even more visually-captivating, as the contrast between the impressionistic/rough-cut visage of Ultimate Ultron and the more humanoid/refined design of Vision would have served to really emphasize what Ultron had lost through the creation of Vision.
Again, I LOVE Ultron Prime's design and I didn't mind how Ultimate Ultron looked, but I just kinda wished they differentiated it more from Ultron Prime to really set them apart as it would have made the differences all the more noticeable.
