Eric Foner, the well-respected historian who teaches at Columbia University, has recently written a book that focuses on Lincoln's views of slavery. Having focused on broad issues of slavery and emancipation in his recent book Forever Free, he now is focusing on Lincoln's personal views on the subject in a new book: The Fiery Trial: Abraham Lincoln and American Slavery.
There is an interview promoting the new book on Columbia's website, including video clips of Foner explaining some of his thoughts on Lincoln, including why he felt the book was a necessary addition to the Lincoln bookshelf. He also has a pretty good answer on one of the key 'what-if' Lincoln questions: What if Lincoln had lived into Reconstruction?
I don't know how much new ground there is for Foner to till in this topic, though his recent study writ large of Reconstruction might allow insights into some of Lincoln's contradictions on the subject. I have little doubt that the book is well written and worth reading for someone interested in reading about Lincoln and slavery for the first time.