Everything reads 3D to me. I really like the shape on the left for some reason.
I think the "correct" values really depend on your light source. These objects feel like they were observed in overcast light. So, like on a cloudy day where the light was diffused there aren't any super harsh shadows. The brighter your light source, the darker the shadows will be.
If you are coming up with random shapes and creating the value for them and wondering what are these values supposed to be you could consider trying a few things.
1) Observe buildings or abstract sculpture images and recreate them as their most basic shapes. Don't worry about details or specific highlights, just the shapes, and then recreate the specific values in your reference image. Make note of what kind of light they are in. Group a few together in your different exercises that go together with different kinds of light.
2) If that's too easy for you, come up with a specific light source you are trying to recreate before diving into this exercise. Then, do the observation exercise marc talks about in Term 1 before you get started. You could search for items in the sun, items in a storm, or on a cloudy day or in a dark room and just observe the values of things for 5 mintues before starting.
-If you want some good reading to go along with these ideas, I'd like to reccomend, "Color and Light" by James Gurney. Lots of good info in there.
All this being said, these are very good if you are just trying to understand the 3D shapes / shadows and how light interacts with these objects. Keep it up!