Personally I highlight three specific areas for improvement:
1- (the most striking point) cut the brightness bust is too bright; I soften a bit, or mark a little fold of clothing which begins in the chest.
2- something more than white glow in the neck muscle just at the height the chin (look better, and give more feeling plaster like the rest).
3- brightness and end above the left eyebrow bust, slightly darker would be better; and the darkest part of that bust left eye, continue it a little more on the edge of the top of the cheek.
Everything else is almost perfect. Congratulations, excelent work!
You have made the wisest artistic choice to study the great masters techniques, it's the only proven way to become one. Genuine talent needs grooming and patience, love and devotion of the craft. I see you have this dedication.
Just yesterday, I spent three hours drawing this same Giuliano with charcoal. And before that, nine hours... I love those curls and the arch of the neck, and the features, but I'm still a beginner and they're hard to capture for me in a satisfying way. How many hours did you work on this, if you say it's 3 months? Seeing this piece is an inspiration... Congrats on the DD.