He was also half in love with Peter Sellers. James Mason complained that Kubrick's indulgence of Sellers' improvisations was allowed to unbalance Lolita and you could say the same about what happens here. Other actors are kept in line but Sellers is allowed to noodle on and on until he's finished. But who can really object? Sellers was a genius.
While we're talking about the acting, I think it's got to be said that George C. Scott is a little over the top. He thinks you've got to telegraph comedy and he's wrong. Slim Pickens, on the other hand is wonderful. Sellers was originally slated to play that role too but chickened out because he wasn't sure it was within his range- and then got very miffed when Pickens made such a good job of it.
Originally the idea was to close with a custard pie fight- the last refuge of the comedy writer who's run out of steam. In the end- at the last moment- Kubrick changed his mind. The ending is abrupt. But no more abrupt than having a bomb dropped on your head.
It's one of the great films, isn't it? A prime contender for any list of the ten best ever. I always have difficulty deciding which is my favourite Kubrick because they're all so good. He's that rare director who made nothing but masterpieces. In the end I think 2001 edges it; it's just so brave and beautiful.