I can't say I was exactly disappointed. Joaquin Phoenix always turns in an outstanding performance and this flick was no exception.
On the other hand, I can't say that much of the movie rendered me ... rapt.
Frances Conroy and Brett Cullen were robbed, IMO. Their characters (Penny Fleck and Thomas Wayne) got basically zero time to do more than flit through scenes as background/motivation. Robert De Niro and his character (Murray Franklin) fared somewhat better but I'd like to have seen more there too.
The film came in right at two hours. Even another 30 minutes, not all of it focused on what's happening inside Arthur Fleck's head, would have rounded out the story.
I dunno. It's just a bummer of a week for me and I begrudged the time wasted on going to a movie today. Maybe I'll like Joker better on a second viewing on the small screen at some point in the future. But as of now, if I was buying permanent viewing rights to a copy of a Joaquin Phoneix picture, I'd go with Inherent Vice.