I recommend people read "Excruciating" (federovsky, 8/30/12) and "Much Ado About Nothing" (Milan, 4/15/2012) if they want to know what they are in store for. "Celine and Julie Go Boating" is difficult, frustrating and over long. However, it is also the kind of film that after seeing it, you wonder what other people have to say about it.
I didn't enjoy it much. Visually, it is not terribly special. The relationship between the two women and the "haunted house" is what keeps us watching, but the scenes come very slowly.
Several people have said it unfolds like a dream. Others have pointed out the lesbian/feminist side to it. Another possibility is that the two women represent two personalities of a schizophrenic nurse who committed an unspeakable crime. That would explain the repetitive cutting between one woman as the nurse and then her counterpart switching in. The two sides of the same madwoman angle possibly explains why the story includes the woman who is a performance amateur subbing for the experienced magician.
Between "Celine" (Juliet Berto) and "Julie" (Dominique Labourier), I think Labourier is the strongest here. Labourier has a lot of charisma; too bad Rivette has her often just laughing directly into the camera.
The characters in the "haunted house" are interesting. Marie-France Pisier is a favorite of mine, and she is very mysterious here.
If the scenes didn't unfold so sluggishly, and if the narrative were tighter, I think it would have been great. Unfortunately, it is too much work to recommend.