Chaplin's last picture is a film with many faults, yet it's not as bad as often claimed. I've seen it many times myself. Here is my opinion of it:
One of the most important flaws is the miscasting of Brando. He seems ill at ease. Thus Loren has to carry the film virtually alone. The whole structure of 'Countess' is not well balanced. There's too much simple visual comedy for a romantic comedy, and vice versa. The plot is thin (It's supposed to be simplistic). Also, the score is at times muddled as previously introduced dramatic themes come and go without any reason (see and hear Hedren's first appearance.) The film is also a bit overlong.
The good things: There are points when the music is up to Chaplin's usually high standards (Cargill's comedy scene, storm theme). Cameo appearances are nice. Direction is more focused and production values are certainly superior to A King in N.Y. Yes, I believe, that what is often described as Chaplin's 'flat' direction due to a lack of skill is an artistic style by choice. Simpleness is not the same as unskilfulness. For instance, during the dance scenes, the camera movement following actors is subtle and economically made. You'll notice it if you watch them in fast-forward.
And if one may feel disappointed at the film on the whole, there's at least a very beautiful, poignant and simple ending that is in my opinion the best of any Chaplin film I've seen. Its every element is in place.
Therefore it's a rather mixed bag of a movie, most suitable for Chaplin fans and very interesting as a curio, at least.