I've created some lessons with complex logic in 19, and found problems with them in 2.0:
Problem 1. If some page does not have questions, it should be displayed for reading. But now one blank page is displayed instead. (problem seems to be @ mod/lesson/view_form.php)
Problem 2. In shortanswer questions i make answers representing typical mistakes, linking to pages in lesson, with description explaining why the answer is incorrect. I grade such answers with 0 points. But now, when answer is graded with 0, then lesson returns to same page, no matter of what is set in Jumps field.
Problem 3. I've entered 2 answers for shortquestion, but it saves 4 answers, making last 2 of them blank. This does not affect logic, but makes it harder to read when all questions are on one page.