Here's a ranked list of general topics that might be found on an eval (the last three are of the least importance by far with the last one being almost not worth putting on the list):
Section structure (lecture review, Q&A, worksheets, demos, group work, etc.)
GSI's skills (board skills, student interaction skills, lecture skills, etc.)
Section content (which topics are covered and how long is spent on each)
Stuff besides section or lecture (i.e. star parties you're at, your TALC, office hours, etc.)
Course content (which topics are covered and how long is spent on each)
Course structure (order of topics, demos during lecture, audience participation during lecture, grading, etc.)
Prof's skills (board skills, student interaction skills, lecture skills, etc.)