Hey Guillermo, great job on these. What I'd say is they're definitely correct, nothing much I'd say about proportion or structure. What I would say is that they're lacking confidence, or personality. They feel a bit timid, like you're doing studies of heads and not art. You're definitely understanding the information objectively, but it doesn't feel like you're injecting much of your own personality into the studies. An exercise I'd recommend trying is to do contour drawings in pen without the intention of doing a "pretty drawing". The point of this is to see how much of the information is integrated into your subconscious drawing process, and too let your brain try out a bunch of different shapes without the fear of failure. If you do do the exercise, let me now! I'd love to see what you come up with. Hope this helps!

omg loving it ! ✌😄