From now on your critiques cannot start with a compliment. That means no more "That looks great" or "Your drawing blows me away."
I am making this rule because the comments are too shallow. You are not getting into observation or analysis or interpretation of the works. Just saying something is good or bad and then giving your advice is OK as far as it goes. But I would not be fair to you unless I demand a more professional level of communication. My job is to make you the best prepared you can be for your creative career! So here is what to do for the rest of the semester:
1. Start with an observation. Describe the drawing as a whole composition. The 4 edges of the page are the edges of the composition. Pretend you are describing the drawing to someone on a phone, a phone without a camera. This forces designers to see each element of a drawing as part of the composition. A skull floating on a white paper is a skull bounded by 4 defining lines forming a rectangle. How big is the skull compared to the rectangle and what is happening in the space around the skull? This helps you to see the figure and the ground in your drawing and if the drawing is part of a design you must consider other elements to be added.
2. Analyze how the artist created the drawing. Make note of the artist's materials, techniques and the results. Analysis is a way to learn from other artists. Some people call it reverse engineering. Answer the question, "How did the artist do that?"
3. Interpret. Give the drawing a name and talk about the story it tells. If the drawing is a sketchy pelvis then the story may be that the artist didn't put in much time into the drawing. If the skull has a dark background maybe the story is a halloween or ghost story, if the skull is floating on a white page then the drawing may be viewed as a clinical study ready for some medical text to be added. Say what the story is to you and why you interpret the drawing this way. There are no right or wrong interpretations. Interpretation provides the artist with the knowledge of how other people see the work. Seeing your work from the outside is essential when you are a professional. Clients and bosses judge your work and won't pay you for it if it doesn't deliver the right message.
4. Summarize: What did you learn from this drawing? What advice would you give to the artist based on your observation, analysis, and interpretation? Summarizing helps other members of your team, in this case, the team is the whole class, know your overall conclusions about the work based on your observation, analysis, and interpretation.