I truly do not understand all of the hate this special is receiving!
I just finished watching this special and I found it very enjoyable. I laughed aloud and found the entire special rather nostalgic as every cast member had worked with another cast member in another/other project(s). I've seen people criticizing Bill's singing, and sure it wasn't perfect, but that is what made it endearing to me. I miss hearing raw and imperfect singing on albums and this gave me just that. Some found it complicated that some actors played themselves where other didn't, but I don't see how this is different from any other celebrity cameo in a television show or movie.
In the end, some with like it and others will not, and I liked it. I just don't know why so many disliked it. This was classic sardonic Bill and in my opinion he delivered.