My son and I are doing this course together. Neither of us has very much experience drawing!
1) My son found it frustrating, but he liked his result. He was glad that he was only doing a pencil drawing and didn't have to do all the colors. He thought it was hard to get the detail on the leaves and shape of the bird. The most challenging part for him were the feet. I enjoyed it, but I realize how many details I have to leave out. Everything was challenging for me!
2) He wouldn't have noticed how many leaves there were. I wouldn't have noticed the brown coloration on the bird's belly or the shape/pattern of the leaves. This definitely would make a difference because I probably couldn't identify either the warbler or the tree without those details.