Letts was great in a small role The Big Short, and while I didn't like the movie, I thought he shined in Lady Bird.
Reilly does an incredible job portraying Buss. Buss is one of these classic promoters that win at life mostly through force of personality rather than brains. His partner Frank, along with his daughter and mother are absolutely critical to keeping him from going off the rails, and when he realizes he is losing one of them, he is crushed. He isn't just losing his mom to dementia, he is losing a critical part of his support network. It is really hard to get a character like Buss right, and Reilly crushes it.
I go back and forth on Adrien Brody in every role. I am still not sure about this one.
I really like DeVaughn Nixon playing his dad. Norm Nixon is one of the more interesting characters in this show, and I wish his story got more screen time.