Menachem Kellner is the author of some absolutely fascinating books on Rambam. I plan to review one of them, Must a Jew Believe Anything? on this website. In the meanwhile, I asked Professor Kellner if he can make the appendix, which deals with Rambam's views on reward and punishment, available for free, and he kindly consented. You can download it here, and you can buy the book here. Happy reading, and Chag Sameach!